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(June 30, 2021)

BASIS

Specifies the electronic basis sets to be used.

TYPE:

STRING

DEFAULT:

No default basis set

OPTIONS:

General, Gen
User defined (*$basis* keyword required).
Symbol
Use standard basis sets as per Chapter 8.
Mixed
Use a mixture of basis sets (see Chapter 8).

RECOMMENDATION:

Consult literature and reviews to aid your selection.

CONCENTRIC_REF_BASIS

Specify the projection basis (PB) in the concentric localization procedure

TYPE:

STRING

DEFAULT:

NONE

OPTIONS:

Parsed in the same way as BASIS; if unspecified, the working basis (WB) will be used as PB.

RECOMMENDATION:

WB is usually a good choice; a smaller basis can chosen with caution to further
reduce the computational cost.

CONCENTRIC_VIRTS_ZETA

Specify the size of the truncated virtual space

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

$m$
The total number of the CL-truncated virtuals is $m\times {n}_{\text{occ}}^{\text{active}}$

RECOMMENDATION:

Use the default; set it to a larger value if higher accuracy is requested.

CONCENTRIC_VIRTS

Use the concentric localization (CL) scheme to truncate the virtual space

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
Use the CL scheme to truncate the virtual space
FALSE
Leave the virtual space untruncated

RECOMMENDATION:

Use CL truncation for WFT-in-DFT calculations.

CVS_IP_ALPHA

Sets the number of ionized target states derived by removing $\alpha $ electron
(M${}_{s}=-\frac{1}{2}$).

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any IP/$\alpha $ states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ ionized states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

CVS_IP_BETA

Sets the number of ionized target states derived by removing $\beta $ electron
(M${}_{s}$=$\frac{1}{2}$, default for CVS-IP).

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any IP/$\beta $ states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ ionized states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

CVS_IP_STATES

Sets the number of core-ionized states to find. By default, $\beta $ electron will be removed.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any IP states.

OPTIONS:

[i,j,k…]
Find $i$ ionized states in the first irrep, $j$ states in the second irrep *etc.*

RECOMMENDATION:

None

DIRECT_DIAG

Perform direct diagonalization to obtain all the NEO excitation energies.

TYPE:

INTEGER

DEFAULT:

0
Use Davidson algorithm.

OPTIONS:

1
Do the direct diagonalization.
0
Use Davidson algorithm.

RECOMMENDATION:

Only use this option when Davidson solutions are not stable.

DISTORT

Specifies whether to apply pressure or external force to a chemical system

TYPE:

LOGICAL

DEFAULT:

False

OPTIONS:

False
Do not use pressure or force
True
Use pressure or force

RECOMMENDATION:

Set to true to apply pressure or force.

EDA2_MOM

Perform ALMO-EDA calculation with non-aufbau electronic configurations
using MOM

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Standard ALMO-EDA calculation
TRUE
ALMO-EDA for non-aufbau states

RECOMMENDATION:

None

EDA_ALIGN_FRGM_SPIN

Turn on the fragment spin alignment procedure

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not performed the spin alignment procedure (turned on by default in unrestricted cases)
1
Perform fragment spin alignment; use GDM for the polarization step preceding the MOM calculations
2
Perform fragment spin alignment; use GDM and perform stability analysis for the polarization step

RECOMMENDATION:

Use 1 or 2 when the radical is of highly symmetric structure

EDA_NOCV

Perform the NOCV analysis and plot the significant NOCVs

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not perform NOCV analysis
1
Plot NOCV pair contributions to density deformation
2
Plot both NOCV pair contribution to density deformation and NOCV orbitals

RECOMMENDATION:

None

EDA_PLOT_DIFF_DEN

Plot changes in electron density due to POL and CT

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not make EDD plots
TRUE
Make EDD plots

RECOMMENDATION:

None

EIGSLV_METH

Control the method for solving the ALMO-CIS eigen-equation

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Explicitly build the Hamiltonian then diagonalize (full-spectrum).
1
Use the Davidson method (currently only available for restricted cases).

RECOMMENDATION:

None

ENV_METHOD

Specify the low-level theory in a projector-based embedding calculation

TYPE:

STRING

DEFAULT:

NONE

OPTIONS:

Parsed in the same way as *$rem* variable “METHOD”

RECOMMENDATION:

A mean-field method (pure or hybrid density functional) should be chosen.

ESP_EFIELD

Triggers the calculation of ESP and/or E-field at nuclear positions or on a given
grid of points

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Compute ESP only
1
Compute both ESP and electric field
2
Compute electric field only

RECOMMENDATION:

None

EX_EDA

Perform an ALMO-EDA calculation with one or more fragments excited.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform EDA with excited-state molecule(s) taken into account.
FALSE

RECOMMENDATION:

None

FODFT_DONOR

Specify the donor fragment in FODFT calculation

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
First fragment as donor
2
Second fragment as donor

RECOMMENDATION:

With FODFT_METHOD = 1, the charged fragment needs to be the
donor fragment

FODFT_METHOD

Specify the flavor of FODFT method

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
FODFT($2\mathrm{n}-1$)@${D}^{+}A$ (HT) / FODFT($2\mathrm{n}+1$)@${D}^{-}A$ (ET)
2
FODFT($2\mathrm{n}$)@$DA$
3
FODFT($2\mathrm{n}-1$)@$DA$ (HT) / FODFT($2\mathrm{n}+1$)@${D}^{-}{A}^{-}$ (ET)

RECOMMENDATION:

The default approach shows the best overall performance

FRAG_DIABAT_DOHT

Specify whether hole or electron transfer is considered

TYPE:

BOOLEAN

DEFAULT:

TRUE

OPTIONS:

TRUE
Do hole transfer
FALSE
Do electron transfer

RECOMMENDATION:

Need to be specified for POD and FODFT calculations

FRAG_DIABAT_METHOD

Specify fragment based diabatization method

TYPE:

STRING

DEFAULT:

NONE

OPTIONS:

ALMO_MSDFT
Perform ALMO(MSDFT) diabatization
POD
Perform projection operator diabatization
ESID
The energy-split-in-dimer method,
^{
1111
}
J. Am. Chem. Soc.

(2006),
128,
pp. 9882.
Link
which is equivalent to
the FMO approach
introduced in Sec. 10.15.2.5
FODFT
Calculate electronic coupling using fragment orbital DFT

RECOMMENDATION:

NONE

FRAG_DIABAT_PRINT

Specify the print level for fragment based diabatization calculations

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
No additional prints
1
Currently it can be used to print out the entire ${\overline{\mathbf{F}}}_{da}$ in POD

RECOMMENDATION:

Use 1 if electron/hole transfer between multiple orbital pairs needs to
considered in POD

GAP_TOL

HOMO/LUMO gap threshold to control whether to shift the diagonal elements of the virtual block of the Fock matrix or not.
If the HOMO/LUMO gap is less than this threshold, at a given SCF iteration, then
the diagonal elements of the virtual block of the Fock matrix are shifted. Otherwise no level-shift is applied.

TYPE:

INTEGER

DEFAULT:

300

OPTIONS:

User-defined

RECOMMENDATION:

The input number must be an integer between 0 and 9999.
The actual threshold is equal to GAP_TOL divided by 1000, in Hartree.
The default value is provided to make the level-shifting calculation run and should not be taken as optimal for any specific problem.
Trial and error may be required to find the optimal threshold.
Larger values of GAP_TOL generally lead to
level-shifting being used more frequently during the SCF convergence process.

GEN_SCFMAN_EMBED

Run a projector-based embedding calculation using the implementation
based onGEN_SCFMAN

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform a projector-based embedding calculation
FALSE
Do not perform an embedding calculation

RECOMMENDATION:

None

GUESS_GRID

Specifies the type of grid to use for SAP guess generation. The options are the same as those of the *$rem* variable XC_GRID.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

0
Use SG-0 for H, C, N, and O; SG-1 for all other atoms.
$n$
Use SG-$n$ for all atoms, $n=1,2$, or 3
$XY$
A string of two six-digit integers $X$ and $Y$, where $X$ is the number of radial points
and $Y$ is the number of angular points where possible numbers of Lebedev angular
points, which must be an allowed value from Table 5.2 in
Section 5.5.
$-XY$
Similar format for Gauss-Legendre grids, with the six-digit integer $X$ corresponding
to the number of radial points and the six-digit integer $Y$ providing the number of
Gauss-Legendre angular points, $Y=2{N}^{2}$.

RECOMMENDATION:

Larger grids may be required if the SAP guess is poor.

JOBTYPE

Specifies the calculation.

TYPE:

STRING

DEFAULT:

Default is single-point, which should be changed to one of the following options.

OPTIONS:

OPT
Equilibrium structure optimization.
TS
Transition structure optimization is currently not available in NEO.
RPATH
Intrinsic reaction path following is currently not available in NEO.

RECOMMENDATION:

Application-dependent. Always use SYM_IGNORE = 1 with geometry optimization.

LEVEL_SHIFT

Determine whether to invoke level-shifting or not together with DIIS.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TURE, FALSE

RECOMMENDATION:

Use TRUE if level-shifting is necessary to accelerate SCF convergence.

LOCAL_CIS

Invoke ALMO-CIS/ALMO-CIS+CT.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Regular CIS
1
ALMO-CIS/ALMO-CIS+CT without RI(slow)
2
ALMO-CIS/ALMO-CIS+CT with RI

RECOMMENDATION:

2 if ALMO-CIS is desired.

LSHIFT

Constant shift applied to all diagonal elements of the virtual block of the Fock matrix.

TYPE:

INTEGER

DEFAULT:

200

OPTIONS:

User-defined

RECOMMENDATION:

The input number must be an integer between 0 and 9999.
The actual shift is equal to GAP_TOL divided by 1000, in Hartree.
The default value is provided to make the level-shifting calculation run and should not be taken as optimal for any specific problem.
Trial and error may be required to find the optimal threshold.
Larger level shifts make the SCF process more stable but also slow down convergence, thus requiring more SCF cycles.

MAX_DP_CYCLES

The maximum number of SCF iterations with damping when SCF_ALGORITHM = DP_DIIS and DP_GDM. See also THRESH_DP_SWITCH.

TYPE:

INTEGER

DEFAULT:

3

OPTIONS:

1
Only a single SCF step with damping, and no damping for the remaining SCF steps.
$n$
$n$ SCF iterations with damping before turning damping off.

RECOMMENDATION:

Increase this number if strong fluctuation continues after damping is turned off.

MAX_LS_CYCLES

The maximum number of DIIS iterations with level-shifting when SCF_ALGORITHM = LS_DIIS. See also THRESH_LS_SWITCH.

TYPE:

INTEGER

DEFAULT:

MAX_SCF_CYCLES

OPTIONS:

1
Only a single DIIS step with level-shifting, and no level-shifting for the remaining DIIS steps.
$n$
$n$ DIIS iterations with level-shifting before turning level-shifting off.

RECOMMENDATION:

None

MAX_SCF_CYCLES

Controls the maximum number of SCF iterations permitted.

TYPE:

INTEGER

DEFAULT:

50

OPTIONS:

$n$
$n>0$ User-selected.

RECOMMENDATION:

Increase for slowly converging systems such as those containing transition
metals.

METHOD

Specifies the exchange-correlation functional.

TYPE:

STRING

DEFAULT:

No default

OPTIONS:

*NAME*
Use METHOD = *NAME*, where *NAME* is one of the following:
HF for Hartree-Fock theory;
one of the DFT methods listed in Section 5.3.4.;

RECOMMENDATION:

In general, consult the literature to guide your selection. Our recommendations for DFT are indicated
in bold in Section 5.3.4.

MOM_METHOD

Determines the target orbitals with which to maximize the overlap on each SCF cycle.

TYPE:

INTEGER

DEFAULT:

MOM

OPTIONS:

MOM
Maximize overlap with the orbitals from the previous SCF cycle.
IMOM
Maximize overlap with the initial guess orbitals.

RECOMMENDATION:

If appropriate guess orbitals can be obtained, then IMOM
can provide more reliable convergence to the desired solution.
^{
59
}
J. Chem. Theory Comput.

(2018),
14,
pp. 1501.
Link

MSDFT_METHOD

Specify the scheme for ALMO(MSDFT)

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

1
The original MSDFT scheme [Eq. (10.129)]
2
The ALMO(MSDFT2) approach [Eq. (10.132)]

RECOMMENDATION:

Use the default method. Note that the method will be automatically
reset to 1 if a meta-GGA functional is requested.

MSDFT_PINV_THRESH

Set the threshold for pseudo-inverse of the interstate overlap

TYPE:

INTEGER

DEFAULT:

4

OPTIONS:

$n$
Set the threshold to 10${}^{-n}$

RECOMMENDATION:

Use the default value

NDAMP

Determine the mixing coefficient. $\alpha $ = NDAMP/100.

TYPE:

INTEGER

DEFAULT:

75

OPTIONS:

User-defined. Integers between 0 and 100.

RECOMMENDATION:

Increase NDAMP if strong fluctuations happen during the SCF process.

NEO_BASIS_LIN_DEP_THRESH

This keyword is used to set the liner dependency threshold for nuclear basis sets. It is defined as ${10}^{-\mathrm{NEO}\mathrm{\_}\mathrm{BASIS}\mathrm{\_}\mathrm{LIN}\mathrm{\_}\mathrm{DEP}\mathrm{\_}\mathrm{THRESH}}$.

TYPE:

DOUBLE

DEFAULT:

5.0

OPTIONS:

User-defined

RECOMMENDATION:

No recommendation.

NEO_EPC

Specifies the electron-proton correlation functional.

TYPE:

STRING

DEFAULT:

No default

OPTIONS:

*NAME*
Use NEO_EPC = *NAME*, where *NAME* can be either epc172 or epc19.

RECOMMENDATION:

Consult the NEO literature to guide your selection.

NEO_E_CONV

Energy convergence criteria in the NEO-SCF calculations so that the difference in energy between electronic and protonic iterations is less than ${10}^{-\mathrm{NEO}\mathrm{\_}\mathrm{E}\mathrm{\_}\mathrm{CONV}}$.

TYPE:

INTEGER

DEFAULT:

8

OPTIONS:

User-defined

RECOMMENDATION:

Tighter criteria for geometry optimization are recommended.

NEO_ISOTOPE

Enable calculations of different types of isotopes. Only one type of isotope is allowed at present.

TYPE:

INTEGER

DEFAULT:

1
Default is the proton isotope.

OPTIONS:

1
This NEO calculation is using proton isotope.
2
This NEO calculation is using deuterium isotope.
3
This NEO calculation is using tritium isotope.

RECOMMENDATION:

Refer to the NEO literature for the best performance on the isotope effects calculations.

NEO_N_SCF_CONVERGENCE

NEO-SCF is considered converged when the nuclear wave function error is less that
${10}^{-\mathrm{NEO}\mathrm{\_}\mathrm{N}\mathrm{\_}\mathrm{SCF}\mathrm{\_}\mathrm{CONVERGENCE}}$.

TYPE:

INTEGER

DEFAULT:

7

OPTIONS:

User-defined

RECOMMENDATION:

None.

NEO_PURECART

This keyword is used to specify Cartesian or spherical Gaussians for nuclear basis functions.

TYPE:

INTEGER

DEFAULT:

2222

OPTIONS:

User-defined

RECOMMENDATION:

Default are Cartesian Gaussians. 1111 would define spherical Gaussians similar to keyword PURECART. Current NEO calculations do not support Cartesian electronic or nuclear basis sets with h angular momentum.

NEO_VPP

Remove $J-K$ terms from the nuclear Fock matrix and the corresponding kernel terms for NEO excited state methods for the case of one quantum proton.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

1
Enable this option.
0
Disable this option.

RECOMMENDATION:

Use this only in the case of one quantum hydrogen.

NEO

Enable a NEO-SCF calculation.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
Enable a NEO-SCF calculation.
FALSE
Disable a NEO-SCF calculation.

RECOMMENDATION:

Set to TRUE if desired.

NN_THRESH

The distance cutoff for neighboring fragments (between which CT is enabled).

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not include interfragment transitions (ALMO-CIS).
$n$
Include interfragment excitations between pairs of fragments the distances between whom
are smaller than $n$ Bohr (ALMO-CIS+CT).

RECOMMENDATION:

None

RR_NO_NORMALISE

Controls whether frequency job calculates resonance-Raman intensities

TYPE:

LOGICAL

DEFAULT:

False

OPTIONS:

False
Normalise RR intensities
True
Doesn’t normalise RR intensities

RECOMMENDATION:

False

SCF_ALGORITHM

Algorithm used for converging the SCF.

TYPE:

STRING

DEFAULT:

DIIS
Pulay DIIS.

OPTIONS:

DIIS
Pulay DIIS.
DM
Direct minimizer.
DIIS_DM
Uses DIIS initially, switching to direct minimizer for later iterations
(See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES).
DIIS_GDM
Use DIIS and then later switch to geometric direct minimization
(See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES).
GDM
Geometric Direct Minimization.
RCA
Relaxed constraint algorithm
RCA_DIIS
Use RCA initially, switching to DIIS for later iterations (see
THRESH_RCA_SWITCH and MAX_RCA_CYCLES described
later in this chapter)
ROOTHAAN
Roothaan repeated diagonalization.

RECOMMENDATION:

In the NEO methods, the GDM procedure is recommended.

SCF_CONVERGENCE

NEO-SCF is considered converged when the electronic wave function error is less that
${10}^{-\mathrm{SCF}\mathrm{\_}\mathrm{CONVERGENCE}}$. Adjust the value of THRESH at the same
time. (Starting with Q-Chem 3.0, the DIIS error is measured by the maximum error
rather than the RMS error as in earlier versions.)

TYPE:

INTEGER

DEFAULT:

5
For single point energy calculations.
8
For geometry optimizations.

OPTIONS:

User-defined

RECOMMENDATION:

None.

SET_ROOTS

Sets the number of NEO excited state roots to find by Davidson or display the number of roots obtained by direct diagonalization.

TYPE:

INTEGER

DEFAULT:

0
Do not look for any excited states.

OPTIONS:

$n$
$n>0$ Looks for $n$ NEO excited states.

RECOMMENDATION:

None

SET_RPA

Do a NEO-TDDFT or NEO-TDHF calculation.

TYPE:

LOGICAL/INTEGER

DEFAULT:

FALSE

OPTIONS:

FALSE
Do a NEO-TDA or NEO-CIS calculation.
TRUE
Do a NEO-TDDFT or NEO-TDHF calculation.

RECOMMENDATION:

Consult the NEO literature to guide your selection.

SPADE_PARTITION

Use the SPADE approach to determine the initial set of embedded (active) orbitals

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
Use SPADE to partition the occupied space
FALSE
Use the Pipek-Mezey localization + Mulliken population to assign occupied orbitals

RECOMMENDATION:

Use SPADE if a significant gap in the spectrum of singular values can be detected.

THRESH_DP_SWITCH

The threshold for turning off damping in SCF iterations is ${10}^{-\text{THRESH\_DP\_SWITCH}}$ when
SCF_ALGORITHM is set to DP_DIIS or DP_GDM. See also MAX_DP_CYCLES.

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

User-defined.

RECOMMENDATION:

None

THRESH_LS_SWITCH

The threshold for turning off level-shifting in DIIS is ${10}^{-\text{THRESH\_LS\_SWITCH}}$ when
SCF_ALGORITHM is set to LS_DIIS. See also MAX_LS_CYCLES.

TYPE:

INTEGER

DEFAULT:

4

OPTIONS:

User-defined.

RECOMMENDATION:

None

UNRESTRICTED

Controls the use of restricted or unrestricted orbitals.

TYPE:

LOGICAL

DEFAULT:

FALSE
Closed-shell systems.
TRUE
Open-shell systems.

OPTIONS:

FALSE
Constrain the spatial part of the alpha and beta orbitals to be the same.
TRUE
Do not Constrain the spatial part of the alpha and beta orbitals.

RECOMMENDATION:

The ROHF method is not available. Note that for unrestricted calculations on
systems with an even number of electrons it is usually necessary to break
$\alpha $/$\beta $ symmetry in the initial guess, by using SCF_GUESS_MIX or
providing *$occupied* information (see Section 4.4 on initial guesses).

VFB_CTA

Use the Variational Forward-Backward (VFB) approach to obtain “one-way” CT PESs.

TYPE:

STRING

DEFAULT:

NONE

OPTIONS:

FORWARD
Allow 1$\to $2 CT only (1 and 2 are two fragments).
BACKWARD
Allow 2$\to $1 CT only.

RECOMMENDATION:

None

XC_GRID

Specifies the type of grid to use for DFT calculations.

TYPE:

INTEGER

DEFAULT:

Functional-dependent; see Table 5.3.

OPTIONS:

0
Use SG-0 for H, C, N, and O; SG-1 for all other atoms.
$n$
Use SG-$n$ for all atoms, $n=1,2$, or 3
$XY$
A string of two six-digit integers $X$ and $Y$, where $X$ is the number of radial points
and $Y$ is the number of angular points where possible numbers of Lebedev angular
points, which must be an allowed value from Table 5.2 in
Section 5.5.
$-XY$
Similar format for Gauss-Legendre grids, with the six-digit integer $X$ corresponding
to the number of radial points and the six-digit integer $Y$ providing the number of
Gauss-Legendre angular points, $Y=2{N}^{2}$.

RECOMMENDATION:

Use the default unless numerical integration problems arise. Larger grids may be
required for optimization and frequency calculations.

FRZN_OPT

Controls whether the job uses zeroed Hessian technique in the frequency calculations

TYPE:

LOGICAL

DEFAULT:

False

OPTIONS:

False
Do not use the zeroed out Hessian
True
Use the zeroed out Hessian

RECOMMENDATION:

False

FRZ_ATOMS

Controls the number of frozen atoms

TYPE:

INTEGER

DEFAULT:

No default

OPTIONS:

User defined

RECOMMENDATION:

None

HARM_FORCE

Sets the force constant for harmonic confiner

TYPE:

INTEGER

DEFAULT:

No default

OPTIONS:

User defined

RECOMMENDATION:

None

HARM_OPT

Controls whether the job uses confining potentials

TYPE:

LOGICAL

DEFAULT:

False

OPTIONS:

False
Do not use the potential
True
Use the potential

RECOMMENDATION:

False

HOATOMS

Controls the number of confined atom

TYPE:

INTEGER

DEFAULT:

No default

OPTIONS:

User defined

RECOMMENDATION:

None

CLENSHAW_NGRID

Number of grid points for the Curtis-Clenshaw quadrature.

TYPE:

INTEGER

DEFAULT:

40

OPTIONS:

RECOMMENDATION:

Use default.

COMPLEX_EXPONENTS

Enable a non-Hermitian calculation with CBFs.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform a non-Hermitian calculation with CBFs

RECOMMENDATION:

Set to TRUE if a non-Hermitian calculation using CBFs is desired.

COMPLEX_METSCF

Specify the NH-SCF solver

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

0
Roothaan iterations
1
DIIS
3
ADIIS
21
Newton-MINRES

RECOMMENDATION:

Use the default (DIIS).

COMPLEX_N_ELECTRON

Add electrons for non-Hermitian calculation.

TYPE:

INTEGER

DEFAULT:

0
Perform the non-Hermitian calculation on $N$-electrons

OPTIONS:

$n$
Perform the non-Hermitian calculation on an $N+n$ electron system

RECOMMENDATION:

None

COMPLEX_SCF_GUESS

Specify the NH-SCF guess

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Use a guess from a static-exchange calculation
1
Read real-basis MO coefficients
2
Read real-basis density matrix
1000
Read guess from a previous calculation

RECOMMENDATION:

Use a guess from a static exchange calculation. Note that for temporary anions, this requires the specification of COMPLEX_TARGET.

COMPLEX_SCF

Perform a non-Hermitian SCF calculation with CBFs

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not perform an NH-SCF calculation
1
Perform a restricted NH-SCF calculation
2
Perform an unrestricted NH-SCF calculation
3
Perform a restricted, open-shell NH-SCF calculation

RECOMMENDATION:

None

COMPLEX_SPIN_STATE

Spin state for non-Hermitian calculation

TYPE:

INTEGER

DEFAULT:

1
Singlet

OPTIONS:

$2S+1$
A state of spin $S$

RECOMMENDATION:

None

COMPLEX_STATIC_EXCHANGE

Perform a CBF static-exchange calculation.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform a static exchange calculation
FALSE
Do not perform a static exchange calculation

RECOMMENDATION:

Set to TRUE if a static-exchange calculation is desired.

COMPLEX_TARGET

Specify the orbital index to be occupied for a temporary anion

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Orbital index (starting at zero) for the additional electron

RECOMMENDATION:

$n$ should always be greater than ${N}_{\text{occ}}-1$.

NOCIS

Run a NOCIS calculation

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

False
Do not run a NOCIS calculation.
True
Run a NOCIS calculation.

RECOMMENDATION:

This variable must be set to true to run a NOCIS or a 1C-NOCIS calculation.

NOCI_DETGEN

Control how the multiple determinants for NOCI are created.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Use only the initial reference determinants.
1
Generate CIS excitations from each reference determinant.
2
Generate all FCI excitations from each reference determinant.
3
Generate $n$ multiple determinants using SCF metadynamics,
where $n$ is given by SCF_SAVEMINIMA = $n$.
4
Generate all CAS excitations from each reference determinant,
where the active orbitals are specified using *$active_orbitals*.

RECOMMENDATION:

By default, these multiple determinants are optimized at the SCF level before
running NOCI. This behaviour can be turned off using by specifying
SKIP_SCFMAN = TRUE.

NOCI_NEIGVAL

The number of NOCI eigenvalues to be printed.

TYPE:

INTEGER

DEFAULT:

10

OPTIONS:

$n$
Positive integer

RECOMMENDATION:

Increase this to print progressively higher NOCI energies.

NOCI_REFGEN

Control how the initial reference determinants are created.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Generate initial reference determinant from a single SCF calculation.
1
Read (multiple) initial reference determinants from a previous calculation.

RECOMMENDATION:

The specific reference determinants to be read from a previous calculation
can be indicated using the *$scf_read* keyword.

NUM_REF

Set the number of atoms (references) to be included in the excitation calculation

TYPE:

Integer

DEFAULT:

None

OPTIONS:

$n$
Positive integer

RECOMMENDATION:

This variable determines the number of references for the calculation. As an example, for the oxygen K-edge in CO${}_{2}$, the number of references would be would be 2 (two oxygen atoms), whereas for carbon it would be 1 (one carbon atom).

ONE_CENTER

Run a 1C-NOCIS calculation

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

False
Run a NOCIS calculation.
True
Run a 1C-NOCIS calculation.

RECOMMENDATION:

This variable must be set to true to run a 1C-NOCIS calculation, and NOCIS must be set to true as well.

ORB_OFFSET

Determine the starting orbital for a NOCIS/STEX/1C-NOCIS calculation

TYPE:

Integer

DEFAULT:

None

OPTIONS:

$n$
Non-negative integer

RECOMMENDATION:

This variable determines the starting orbital for the calculation. As an example, for the oxygen K-edge in CO${}_{2}$, the starting orbital would be 0, whereas for carbon it would be 2.

SCF_EESCALE_ARG

Control the phase angle of the complex $\lambda $ electron-electron scaling.

TYPE:

INTEGER

DEFAULT:

$00000$ meaning $0.0000$

OPTIONS:

$abcde$ corresponding to $a.bcde$

RECOMMENDATION:

A complex phase angle of $00500$, meaning $0.0500$, is usually
sufficient to follow a solution safely past the Coulson-Fischer point
and onto its complex holomorphic counterpart.

SCF_EESCALE_MAG

Control the magnitude of the $\lambda $ electron-electron scaling.

TYPE:

INTEGER

DEFAULT:

$10000$ meaning $1.0000$

OPTIONS:

$abcde$ corresponding to $a.bcde$

RECOMMENDATION:

For holomorphic Hartree-Fock orbitals, only the magnitude of the input is used, while
for real Hartree-Fock orbitals, the input sign indicates the sign of $\lambda $.

SCF_HOLOMORPHIC

Turn on the use of holomorphic Hartree-Fock orbitals.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Holomorphic Hartree-Fock is turned off
TRUE
Holomorphic Hartree-Fock is turned on.

RECOMMENDATION:

If TRUE, holomorphic Hartree-Fock complex orbital coefficients will always be used.
If FALSE, but COMPLEX = TRUE, complex Hermitian orbitals will be used.

STEX

Run a STEX calculation

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

False
Do not run a STEX calculation.
True
Run a STEX calculation.

RECOMMENDATION:

This variable must be set to true to run a STEX calculation. NOCIS cannot be set to true.

USE_LIBNLQ

Turn on the use of LIBNLQ for calculating nonlocal correlation funcitonal.

TYPE:

LOGICAL

DEFAULT:

True
For VV10.
FALSE
For all other nonlocal funcitonals.

OPTIONS:

False
True

RECOMMENDATION:

Use the default

USE_LIBNOCI

Turn on the use of LIBNOCI for running NOCI calculations.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

False
Do not use LIBNOCI (uses original Q-Chem implementation).
True
Use the LIBNOCI implementation.

RECOMMENDATION:

The *$rem* variables detailed below are only available in LIBNOCI.

PLOT_ALMO_FRZ

Plot ALMOs at the frozen stage of EDA2 calculations

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not plot frozen ALMOs
TRUE
Plot frozen ALMOs

RECOMMENDATION:

None

PLOT_ALMO_POL

Plot ALMOs after the polarization calculation

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not plot polarized ALMOs
TRUE
Plot polarized ALMOs

RECOMMENDATION:

None

FDIFF_STEPSIZE

Displacement used for calculating derivatives by finite difference.

TYPE:

INTEGER

DEFAULT:

1
Corresponding to $1.88973\times {10}^{-5}$ a.u.

OPTIONS:

$n$
Use a step size of $n$ times the default value.

RECOMMENDATION:

Use the default unless problems arise.

RESPONSE_POLAR

Control the use of analytic or numerical polarizabilities.

TYPE:

INTEGER

DEFAULT:

0 or $-$1
= 0 for HF or DFT, $-$1 for all other methods

OPTIONS:

0
Perform an analytic polarizability calculation.
$-$1
Perform a numeric polarizability calculation even when analytic 2nd derivatives are available.

RECOMMENDATION:

None

ADC_CAP

Controls the type of CAP/ADC calculation to be performed.

TYPE:

INTEGER

DEFAULT:

0
Do not perform a CAP/ADC calculation.

OPTIONS:

1
Perform a subspace-projected CAP/ADC calculation.

RECOMMENDATION:

Set to 1 for the computation of CAP/ADC subspace projections.

ADC_CVS

Activates the use of the CVS approximation for the calculation of CVS-ADC
core-excited states.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Activates the CVS approximation.
FALSE
Do not compute core-excited states using the CVS approximation.

RECOMMENDATION:

Set to TRUE, if to obtain core-excited states for the simulation of
X-ray absorption spectra. In the case of TRUE, the *$rem* variable
CC_REST_OCC has to be defined as well.

ADC_C_C

Set the spin-opposite scaling parameter ${c}_{c}$ for the ADC(2) calculation.
The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.

TYPE:

INTEGER

DEFAULT:

1170
Optimized value ${c}_{c}=1.17$ for ADC(2)-s or
1000
${c}_{c}=1.0$ for ADC(2)-x

OPTIONS:

$n$
Corresponding to $n\cdot {10}^{-3}$

RECOMMENDATION:

Use the default.

ADC_C_T

Set the spin-opposite scaling parameter ${c}_{T}$ for an SOS-ADC(2) calculation.
The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.

TYPE:

INTEGER

DEFAULT:

1300
Optimized value ${c}_{T}=1.3$.

OPTIONS:

$n$
Corresponding to $n\cdot {10}^{-3}$

RECOMMENDATION:

Use the default.

ADC_C_X

Set the spin-opposite scaling parameter ${c}_{x}$ for the ADC(2)-x calculation.
The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.

TYPE:

INTEGER

DEFAULT:

1300
Optimized value ${c}_{x}=0.9$ for ADC(2)-x.

OPTIONS:

$n$
Corresponding to $n\cdot {10}^{-3}$

RECOMMENDATION:

Use the default.

ADC_DAVIDSON_CONV

Controls the convergence criterion of the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

$6$
Corresponding to ${10}^{-6}$

OPTIONS:

$n\le 12$
Corresponding to ${10}^{-n}$.

RECOMMENDATION:

Use the default unless higher accuracy is required or convergence problems are encountered.

ADC_DAVIDSON_MAXITER

Controls the maximum number of iterations of the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

60

OPTIONS:

$n$
Number of iterations

RECOMMENDATION:

Use the default unless convergence problems are encountered.

ADC_DAVIDSON_MAXSUBSPACE

Controls the maximum subspace size for the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

$5\times $ the number of excited states to be calculated.

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Should be at least 2–4$\times $ the number of excited states to calculate. The
larger the value the more disk space is required.

ADC_DAVIDSON_THRESH

Controls the threshold for the norm of expansion vectors to be added
during the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

Twice the value of ADC_DAVIDSON_CONV, but at maximum ${10}^{-14}$.

OPTIONS:

$n\le 14$
Corresponding to ${10}^{-n}$

RECOMMENDATION:

Use the default unless convergence problems are encountered. The threshold
value ${10}^{-n}$ should always be smaller than the convergence criterion
ADC_DAVIDSON_CONV.

ADC_DENSITY_MAXITER

When setting ADC_DENSITY_ORDER = 4, this keyword controls the maximum number
of DIIS iterations carried out in the $\mathrm{\Sigma}(4+)$ procedure.

TYPE:

INTEGER

DEFAULT:

1000

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Use the default value.

ADC_DENSITY_ORDER

Controls the order of the ground state density used for the computation of
third-order ADC matrix elements (non-CVS methods only).

TYPE:

INTEGER

DEFAULT:

2
Use strict third-order ADC(3) schemes.

OPTIONS:

3
Use a third-order ground state density computed from the IP-ADC(3)
effective transition moments and the corresponding
fourth order static self-energy according to the $\mathrm{\Sigma}(4)$ scheme
4
Use an improved third-order ground state density and the corresponding
improved fourth-order static self-energy computed according to the
self-consistent $\mathrm{\Sigma}(4+)$ procedure

RECOMMENDATION:

In case of IP-ADC(3) calculations, employing the $\mathrm{\Sigma}(4+)$ scheme
provides more accurate ionization potentials and ionized state dipole
moments.

ADC_DIIS_ECONV

Controls the convergence criterion for the excited state energy during DIIS.

TYPE:

INTEGER

DEFAULT:

6
Corresponding to ${10}^{-6}$

OPTIONS:

$n$
Corresponding to ${10}^{-n}$

RECOMMENDATION:

None

ADC_DIIS_MAXITER

Controls the maximum number of DIIS iterations.

TYPE:

INTEGER

DEFAULT:

50

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Increase in case of slow convergence.

ADC_DIIS_RCONV

Convergence criterion for the residual vector norm of the excited state during DIIS.

TYPE:

INTEGER

DEFAULT:

6
Corresponding to ${10}^{-6}$

OPTIONS:

$n$
Corresponding to ${10}^{-n}$

RECOMMENDATION:

None

ADC_DIIS_SIZE

Controls the size of the DIIS subspace.

TYPE:

INTEGER

DEFAULT:

7

OPTIONS:

$n$
User-defined integer

RECOMMENDATION:

None

ADC_DIIS_START

Controls the iteration step at which DIIS is turned on.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Set to a large number to switch off DIIS steps.

ADC_DIRECT

For third-order ADC methods, this keyword controls if some large intermediate tensor
contractions should be carried out in advance and the result saved in memory for later use
or if these quantities should be evaluated directly whenever they are encountered.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Directly evaluate some ${N}^{6}$-scaling tensor contractions. This will reduce the memory
requirement by $\sim $10 %.
FALSE
Precompute all possible ${N}^{6}$-scaling intermediates. This will speed up ADC(3)
calculations considerably (by a factor of $\sim $3 in case of ADC(3) for
$N$-electron excitations and somewhat less for IP- and EA-ADC(3)).

RECOMMENDATION:

Use the default value unless memory is the bottleneck.

ADC_DO_DIIS

Activates the use of the DIIS algorithm for the calculation of ADC(2) excited states.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Use DIIS algorithm.
FALSE
Do diagonalization using Davidson algorithm.

RECOMMENDATION:

None.

ADC_DO_DYSON

Controls if Dyson orbitals are output in case of IP- and EA-ADC calculations. This
keyword only takes effect when used together with STATE_ANALYSIS = TRUE.
See Section. 10.2.6 for further details.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Output Dyson orbitals as cube files.
FALSE
Do not output Dyson orbitals.

RECOMMENDATION:

Set to TRUE if visualization of ionization/electron-attachment processes is
desired.

ADC_NGUESS_DOUBLES

Controls the number of excited state guess vectors which are double excitations,
two-hole-one-particle ionizations and one-hole-two-particle electron-attachments in case
of ADC, IP-ADC and EA-ADC, respectively.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

ADC_NGUESS_SINGLES

Controls the number of excited state guess vectors which are single excitations, one-hole
ionizations and one-particle electron-attachments in case of ADC, IP-ADC and EA-ADC,
respectively. If the
number of requested excited states exceeds the total number of guess vectors (singles and
doubles), this parameter is automatically adjusted, so that the number of guess vectors
matches the number of requested excited states.

TYPE:

INTEGER

DEFAULT:

Equals to the number of excited states requested.

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Increase if there are convergence problems.

ADC_PRINT

Controls the amount of printing during an ADC calculation.

TYPE:

INTEGER

DEFAULT:

1
Basic status information and results are printed.

OPTIONS:

0
Quiet: almost only results are printed.
1
Normal: basic status information and results are printed.
2
Debug: more status information, extended information on timings.
…

RECOMMENDATION:

Use the default.

ADC_PROP_ES2ES

Controls the calculation of transition properties between excited, ionized or
electron-attached states (currently only transition dipole moments and oscillator strengths). For ADC for
$N$-electron excitations, this keyword also controls
the computation of two-photon absorption cross-sections of excited states
using the sum-over-states expression.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Calculate state-to-state transition properties.
FALSE
Do not compute transition properties between excited, ionized or
electron-attached states.

RECOMMENDATION:

Set to TRUE, if state-to-state properties (ADC, IP-ADC, EA-ADC) or sum-over-states two-photon
absorption cross-sections (only ADC) are required.

ADC_PROP_ES

Controls the calculation of excited, ionized or electron-attached state properties
(currently only dipole moments and ${\widehat{r}}^{2}$ expectation values).

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Calculate excited, ionized or electron-attached state properties.
FALSE
Do not compute state properties.

RECOMMENDATION:

Set to TRUE, if properties are required.

ADC_PROP_TPA

Controls the calculation of two-photon absorption cross-sections of excited states using
matrix inversion techniques.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Calculate two-photon absorption cross-sections.
FALSE
Do not compute two-photon absorption cross-sections.

RECOMMENDATION:

Set to TRUE, if to obtain two-photon absorption cross-sections.

ADC_STRICT_ISR

Controls how second-order ground state contributions are treated in the calculation of
second- and third-order IP- and EA-ADC state properties using the second-order ISR
formalism.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Scale the second-order part of the ground state contribution to one-electron
properties of ionized/electron-attached states by the
one-hole/one-particle character of the respective states
as implied by the strict ISR derivation.
FALSE
Use the full second-order ground state contribution for each
ionized/electron-attached state property.

RECOMMENDATION:

Use the default value. Both options are, however, valid second-order treatments of
ionized/electron-attached state properties and should yield very similar results for
states with predominant one-hole/one-particle chaaracter.

ADD_CHARGED_CAGE

Add a point charge cage of a given radius and total charge.

TYPE:

INTEGER

DEFAULT:

0
No cage.

OPTIONS:

0
No cage.
1
Dodecahedral cage.
2
Spherical cage.

RECOMMENDATION:

Spherical cage is expected to yield more accurate results, especially for small radii.

AFSSH

Adds decoherence approximation to surface hopping calculation.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Traditional surface hopping, no decoherence.
1
Use augmented fewest-switches surface hopping (AFSSH).

RECOMMENDATION:

AFSSH will increase the cost of the calculation, but may improve accuracy
for some systems. See Refs. 1060, 1063, 602
for more detail.

AIFDEM_CTSTATES

Include charge-transfer-like cation/anion pair states
in the AIFDEM basis.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Include CT states.
FALSE
Do not include CT states.

RECOMMENDATION:

None

AIFDEM_EMBED_RANGE

Specifies the size of the QM region for charge embedding

TYPE:

INTEGER

DEFAULT:

FULL_QM

OPTIONS:

FULL_QM
No charge embedding.
0
Treat only excited fragments with QM.
$n$
Range (in Å) from excited fragments within which to
treat other fragments with QM.

RECOMMENDATION:

The minimal threshold of zero Å typically
maintains accuracy while significantly reducing computational time.

AIFDEM_FRGM_READ

Skips fragment scf calculations.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Skips fragment scf calculations, only computation of matrix elements.
FALSE
Regular AIFDEM calculation as specified by other REM variables.

RECOMMENDATION:

Requires a prior calculation that computes fragment scf data.

AIFDEM_FRGM_WRITE

Fragment SCF calculations only.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Only fragment scf calculations are carried out, no computation of matrix elements.
FALSE
Regular AIFDEM calculation as specified by other REM variables.

RECOMMENDATION:

None

AIFDEM_NTOTHRESH

Controls the number of NTOs that are retained in the
exciton-site basis states.

TYPE:

INTEGER

DEFAULT:

99

OPTIONS:

$n$
Threshold percentage of the norm of fragment NTO amplitudes.

RECOMMENDATION:

A threshold of $85\%$ gives a good trade-off of computational time and
accuracy for organic molecules.

AIFDEM_SEGEND

Indicates the index of the last matrix element to be computed.

TYPE:

INTEGER

DEFAULT:

NONE

OPTIONS:

$n$
Last matrix element of chunk to be computed.

RECOMMENDATION:

Needs to be used with AIFDEM_SEGSTART

AIFDEM_SEGSTART

Indicates the index of the first matrix element to be computed.

TYPE:

INTEGER

DEFAULT:

NONE

OPTIONS:

$n$
First matrix element of chunk to be computed.

RECOMMENDATION:

Needs to be used with AIFDEM_SEGEND

AIFDEM_SINGFIS

Include multiexciton states
in the AIFDEM basis.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Include multiexciton states.
FALSE
Do not include multiexciton states.

RECOMMENDATION:

None

AIFDEM

Perform an AIFDEM calculation.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not perform an AIFDEM calculation.
TRUE
Perform an AIFDEM calculation.

RECOMMENDATION:

False

AIMD_FICT_MASS

Specifies the value of the fictitious electronic mass $\mu $, in atomic units,
where $\mu $ has dimensions of (energy)$\times $(time)${}^{2}$.

TYPE:

INTEGER

DEFAULT:

None

OPTIONS:

User-specified

RECOMMENDATION:

Values in the range of 50–200 a.u. have been employed in test calculations;
consult Ref. 443 for examples and discussion.

AIMD_INIT_VELOC_NANO_RANDOM

Uses a more precise random seed for generating random initial velocities.

TYPE:

LOGICAL

DEFAULT:

TRUE
Use a more precise random seed.

OPTIONS:

FALSE
Use a less precise random seed.

RECOMMENDATION:

Leave this set to TRUE unless necessary.
This option determines the source of the random seed used for sampling random
initial velocities when AIMD_INIT_VELOC requires such.
Setting the option to FALSE will have the seed based on the system time in
seconds, meaning that two otherwise identical simulations starting in
the same second will produce identical initial velocities.
With the option set to TRUE, such collisions are virtually impossible.
The option is kept for legacy purposes. There should rarely ever be a need
to set it to FALSE.

AIMD_INIT_VELOC

Specifies the method for selecting initial nuclear velocities.

TYPE:

STRING

DEFAULT:

None

OPTIONS:

THERMAL
Random sampling of nuclear velocities from a Maxwell-Boltzmann
distribution. The user must specify the temperature in Kelvin via
the *$rem* variable AIMD_TEMP.
ZPE
Choose velocities in order to put zero-point vibrational energy into
each normal mode, with random signs. This option requires that a
frequency job to be run beforehand.
QUASICLASSICAL
Puts vibrational energy into each normal mode. In contrast to the
ZPE option, here the vibrational energies are sampled from a
Boltzmann distribution at the desired simulation temperature. This
also triggers several other options, as described below.

RECOMMENDATION:

This variable need only be specified in the event that velocities are not
specified explicitly in a *$velocity* section.

AIMD_LANGEVIN_TIMESCALE

Sets the timescale (strength) of the Langevin thermostat

TYPE:

INTEGER

DEFAULT:

none

OPTIONS:

$n$
Thermostat timescale,asn $n$ fs

RECOMMENDATION:

Smaller values (roughly 100) equate to tighter thermostats but may inhibit
rapid sampling. Larger values ($\ge 1000$) allow for more rapid sampling but
may take longer to reach thermal equilibrium.

AIMD_METHOD

Selects an ab initio molecular dynamics algorithm.

TYPE:

STRING

DEFAULT:

BOMD

OPTIONS:

BOMD
Born-Oppenheimer molecular dynamics.
CURVY
Curvy-steps Extended Lagrangian molecular dynamics.

RECOMMENDATION:

BOMD yields exact classical molecular dynamics, provided that the energy is
tolerably conserved. ELMD is an approximation to exact classical dynamics whose
validity should be tested for the properties of interest.

AIMD_MOMENTS

Requests that multipole moments be output at each time step.

TYPE:

INTEGER

DEFAULT:

0
Do not output multipole moments.

OPTIONS:

$n$
Output the first $n$ multipole moments.

RECOMMENDATION:

None

AIMD_NUCL_DACF_POINTS

Number of time points to use in the dipole auto-correlation function for an AIMD trajectory

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not compute dipole auto-correlation function.
$1\le n\le \text{AIMD\_STEPS}$
Compute dipole auto-correlation function for last $n$
timesteps of the trajectory.

RECOMMENDATION:

If the DACF is desired, set equal to AIMD_STEPS.

AIMD_NUCL_SAMPLE_RATE

The rate at which sampling is performed for the velocity and/or dipole
auto-correlation function(s). Specified as a multiple of steps; *i.e.*,
sampling every step is 1.

TYPE:

INTEGER

DEFAULT:

None.

OPTIONS:

$1\le n\le \text{AIMD\_STEPS}$
Update the velocity/dipole auto-correlation function
every $n$ steps.

RECOMMENDATION:

Since the velocity and dipole moment are routinely calculated for *ab initio* methods,
this variable should almost always be set to 1 when the VACF/DACF are desired.

AIMD_NUCL_VACF_POINTS

Number of time points to use in the velocity auto-correlation function for
an AIMD trajectory

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not compute velocity auto-correlation function.
$1\le n\le \text{AIMD\_STEPS}$
Compute velocity auto-correlation function for last $n$
time steps of the trajectory.

RECOMMENDATION:

If the VACF is desired, set equal to AIMD_STEPS.

AIMD_QCT_INITPOS

Chooses the initial geometry in a QCT-MD simulation.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$0$
Use the equilibrium geometry.
$n$
Picks a random geometry according to the harmonic vibrational wave function.
$-n$
Generates $n$ random geometries sampled from
the harmonic vibrational wave function.

RECOMMENDATION:

None.

AIMD_QCT_WHICH_TRAJECTORY

Picks a set of vibrational quantum numbers from a random distribution.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

$n$
Picks the $n$th set of random initial velocities.
$-n$
Uses an average over $n$ random initial velocities.

RECOMMENDATION:

Pick a positive number if you want the initial velocities to correspond
to a particular set of vibrational occupation numbers and choose a
different number for each of your trajectories. If initial velocities
are desired that corresponds to an average over $n$ trajectories, pick a
negative number.

AIMD_SHORT_TIME_STEP

Specifies a shorter electronic time step for FSSH calculations.

TYPE:

INTEGER

DEFAULT:

TIME_STEP

OPTIONS:

$n$
Specify an electronic time step duration of $n$/AIMD_TIME_STEP_CONVERSION
a.u. If $n$ is less than the nuclear time step variable TIME_STEP, the
electronic wave function will be integrated multiple times per nuclear time step,
using a linear interpolation of nuclear quantities such as the energy gradient and
derivative coupling. Note that $n$ must divide TIME_STEP evenly.

RECOMMENDATION:

Make AIMD_SHORT_TIME_STEP as large as possible while keeping the trace of
the density matrix close to unity during long simulations. Note that while specifying an
appropriate duration for the electronic time step is essential for maintaining accurate
wave function time evolution, the electronic-only time steps employ linear interpolation
to estimate important quantities. Consequently, a short electronic time step is not a
substitute for a reasonable nuclear time step.

AIMD_STEPS

Specifies the requested number of molecular dynamics steps.

TYPE:

INTEGER

DEFAULT:

None.

OPTIONS:

User-specified.

RECOMMENDATION:

None.

AIMD_TEMP

Specifies a temperature (in Kelvin) for Maxwell-Boltzmann velocity sampling.

TYPE:

INTEGER

DEFAULT:

None

OPTIONS:

User-specified number of Kelvin.

RECOMMENDATION:

This variable is only useful in conjunction with AIMD_INIT_VELOC =
THERMAL. Note that the simulations are run at constant energy, rather than
constant temperature, so the mean nuclear kinetic energy will fluctuate in the
course of the simulation.

AIMD_THERMOSTAT

Applies thermostatting to AIMD trajectories.

TYPE:

INTEGER

DEFAULT:

none

OPTIONS:

LANGEVIN
Stochastic, white-noise Langevin thermostat
NOSE_HOOVER
Time-reversible, Nosé-Hoovery chain thermostat

RECOMMENDATION:

Use either thermostat for sampling the canonical (NVT) ensemble.

AIMD_TIME_STEP_CONVERSION

Modifies the molecular dynamics time step to increase granularity.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

$n$
The molecular dynamics time step is TIME_STEP/$n$ a.u.

RECOMMENDATION:

None

AIRBED_ALPHA

Sets the value of $\alpha $.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Corresponding to $\alpha $ = $n/1000$

RECOMMENDATION:

0 or -1200 for hBN surface

AIRBED

Perform an AIRBED calculation.

TYPE:

BOOLEAN

DEFAULT:

False

OPTIONS:

True
Perform an AIRBED calculation.
False
Don’t perform an AIRBED calculation.

RECOMMENDATION:

Set the *$rem* variable DFT_D to EMPIRICAL_GRIMME.

ANHAR_SEL

Select a subset of normal modes for subsequent anharmonic frequency analysis.

TYPE:

LOGICAL

DEFAULT:

FALSE
Use all normal modes

OPTIONS:

TRUE
Select subset of normal modes

RECOMMENDATION:

None

ANHAR

Performing various nuclear vibrational theory (TOSH, VPT2, VCI) calculations
to obtain vibrational anharmonic frequencies.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Carry out the anharmonic frequency calculation.
FALSE
Do harmonic frequency calculation.

RECOMMENDATION:

Since this calculation involves the third and fourth derivatives at the
minimum of the potential energy surface, it is recommended that the
GEOM_OPT_TOL_DISPLACEMENT, GEOM_OPT_TOL_GRADIENT and
GEOM_OPT_TOL_ENERGY tolerances are set tighter. Note that VPT2
calculations may fail if the system involves accidental degenerate resonances.
See the VCI *$rem* variable for more details about increasing the
accuracy of anharmonic calculations.

ANTIBOND

Triggers Antibond subroutine to generate antibonding orbitals after a converged SCF

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Does not localize the virtual space.
1
Localizes the virtual space, one antibonding for every bond.
2,3
Fill the virtual space with antibonding orbitals-like guesses.
4
Does Frozen Natural Orbitals and leaves them on scratch for future jobs or visualization.

RECOMMENDATION:

None

ARI_R0

Determines the value of the inner fitting radius (in Ångstroms)

TYPE:

INTEGER

DEFAULT:

4
A value of 4 Å will be added to the atomic van der Waals radius.

OPTIONS:

$n$
User defined radius.

RECOMMENDATION:

For some systems the default value may be too small and the calculation will become unstable.

ARI_R1

Determines the value of the outer fitting radius (in Ångstroms)

TYPE:

INTEGER

DEFAULT:

5
A value of 5 Å will be added to the atomic van der Waals radius.

OPTIONS:

$n$
User defined radius.

RECOMMENDATION:

For some systems the default value may be too small and the calculation will become unstable. This value also determines, in part, the smoothness of the potential energy surface.

ARI

Toggles the use of the atomic resolution-of-the-identity (ARI) approximation.

TYPE:

LOGICAL

DEFAULT:

FALSE
ARI will not be used by default for an RI-JK calculation.

OPTIONS:

TRUE
Turn on ARI.

RECOMMENDATION:

For large (especially 1D and 2D) molecules the approximation may yield significant improvements in Fock evaluation time.

ASCI_CDETS

Specifies the number of determinants to search over during ASCI wavefunction growth steps.

TYPE:

INTEGER

DEFAULT:

-5

OPTIONS:

$N>0$
search from the top $N$ determinants
$$
search from the top determinants whose cumulative weight in the wavefunction corresponds to $1-{2}^{N}$

RECOMMENDATION:

Using a dynamically determined value ($$) gives better results.

ASCI_DAVIDSON_GUESS

Specifies the truncated CI guess used for ASCI’s Davidson solver.

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

$N$
Order of the truncated CI to solve explicitly ASCI Davidson guess.

RECOMMENDATION:

Accurate excited states and rapid convergence of the ground state benefit from a good zero-order guess for the low energy spectrum. The default is often sufficient.

ASCI_DIAG

Specifies the diagonalization procedure.

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

1
Davidson solver
2
Eigen sparse matrix solver

RECOMMENDATION:

Use 2 for best trade-off of speed and memory usage. If memory usage becomes to great, switch to 1.

ASCI_NDETS

Specifies the number of determinants to include in the ASCI wavefunction.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$N$
for a wavefunction with $N$ determinants

RECOMMENDATION:

Typical ASCI expansions range from 50,000 to 2,000,000 determinants depending on active space size, complexity of problem, and desired accuracy

ASCI_RESTART

Specifies whether to initialize the ASCI wavefunction with the wf_data file.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
read CI coefficients from the wf_data file
FALSE
do not read the CI coefficients from disk

RECOMMENDATION:

ASCI_SKIP_PT2

Specifies whether ASCI PT2 correction should be calculated.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
compute ASCI PT2 contribution
TRUE
do not compute ASCI PT2 contribution

RECOMMENDATION:

The PT2 correction is essential to obtaining converged ASCI energies.

ASCI_SPIN_PURIFY

Indicates whether or not the ASCI wavefunction should be augmented with missing
determinants to ensure a spin-pure state.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
augment the wavefunction with determinants to ensure a spin eigenstate
FALSE
do not augment the wavefunction

RECOMMENDATION:

ASCI_USE_NAT_ORBS

Specifies whether rotation to a natural orbital basis should be carried out between growth steps.

TYPE:

BOOLEAN

DEFAULT:

TRUE

OPTIONS:

TRUE
rotate to a natural orbital basis between growth wavefunction growth steps
FALSE
do not rotate to a natural orbital basis

RECOMMENDATION:

Natural orbital rotations significantly improve the compactness and therefore accuracy of the ASCI wavefunction.

AUX_BASIS_CORR

Sets the auxiliary basis set for RI-MP2 to be used or invokes RI-MP2 in case of double-hybrid DFT or MP2

TYPE:

STRING

DEFAULT:

No default auxiliary basis set

OPTIONS:

General, Gen
User-defined. As for BASIS
Symbol
Use standard auxiliary basis sets as in the table below
Mixed
Use a combination of different basis sets

RECOMMENDATION:

Consult literature and Basis Set Exchange to aid your selection.

AUX_BASIS_J

Sets the auxiliary basis set for RI-J to be used or invokes RI-J

TYPE:

STRING

DEFAULT:

No default auxiliary basis set

OPTIONS:

General, Gen
User-defined. As for BASIS
Symbol
Use standard auxiliary basis sets as in the table below
Mixed
Use a combination of different basis sets

RECOMMENDATION:

Consult literature and Basis Set Exchange to aid your selection.

AUX_BASIS_K

Sets the auxiliary basis set for RI-K or occ-RI-K to be used or invokes occ-RI-K

TYPE:

STRING

DEFAULT:

No default auxiliary basis set

OPTIONS:

General, Gen
User-defined. As for BASIS
Symbol
Use standard auxiliary basis sets as in the table below
Mixed
Use a combination of different basis sets

RECOMMENDATION:

Consult literature and Basis Set Exchange to aid your selection.

AUX_BASIS

Sets the auxiliary basis set to be used

TYPE:

STRING

DEFAULT:

No default auxiliary basis set

OPTIONS:

General, Gen
User-defined. As for BASIS
Symbol
Use standard auxiliary basis sets as in the table below
Mixed
Use a combination of different basis sets

RECOMMENDATION:

Consult literature and Basis Set Exchange to aid your selection.

BASIS2

Defines the (small) second basis set.

TYPE:

STRING

DEFAULT:

No default for the second basis set.

OPTIONS:

Symbol
Use standard basis sets as for BASIS.
BASIS2_GEN
General BASIS2
BASIS2_MIXED
Mixed BASIS2

RECOMMENDATION:

BASIS2 should be smaller than BASIS. There is little advantage to using
a basis larger than a minimal basis when BASIS2 is used for initial guess purposes.
Larger, standardized BASIS2 options are available for dual-basis calculations
as discussed in Section 4.7 and summarized in Table 4.2.

BASISPROJTYPE

Determines which method to use when projecting the density matrix of
BASIS2

TYPE:

STRING

DEFAULT:

FOPPROJECTION (when DUAL_BASIS_ENERGY=false)
OVPROJECTION (when DUAL_BASIS_ENERGY=true)

OPTIONS:

FOPPROJECTION
Construct the Fock matrix in the second basis
OVPROJECTION
Projects MOs from BASIS2 to BASIS.

RECOMMENDATION:

None

BASIS_LIN_DEP_THRESH

Sets the threshold for determining linear dependence in the basis set

TYPE:

INTEGER

DEFAULT:

6
Corresponding to a threshold of ${10}^{-6}$

OPTIONS:

$n$
Sets the threshold to ${10}^{-n}$

RECOMMENDATION:

Set to 5 or smaller if you have a poorly behaved SCF and you suspect linear
dependence in you basis set. Lower values (larger thresholds) may affect the
accuracy of the calculation.

BASIS

Sets the basis set to be used

TYPE:

STRING

DEFAULT:

No default basis set

OPTIONS:

General, Gen
User-defined. See section below
Symbol
Use standard basis sets as in the table below
Mixed
Use a combination of different basis sets

RECOMMENDATION:

Consult literature and reviews to aid your selection.

BECKE_SHIFT

Controls atomic cell shifting in determination of Becke weights.

TYPE:

STRING

DEFAULT:

BRAGG_SLATER

OPTIONS:

UNSHIFTED
Use the original weighting scheme of Becke (bisection point).
BRAGG_SLATER
Use the empirically derived Bragg-Slater radii.
UNIVERSAL_DENSITY
Use the ab initio derived Pacios radii.

RECOMMENDATION:

If interested in the partitioning of the default atomic quadrature, use UNSHIFTED.
If using for physical interpretation, choose BRAGG_SLATER or UNIVERSAL_DENSITY.
All cDFT calculations and calculations where POP_BECKE=TRUE
will default to BRAGG_SLATER radii, otherwise the default grid is UNSHIFTED.

BONDED_EDA

Use the bonded ALMO-EDA.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not perform bonded ALMO-EDA.
1
Perform ALMO-EDA with non-orthogonal CI.
2
Perform ALMO-EDA with spin-projected formalism.

RECOMMENDATION:

Set to 2 for all cases where the supersystem is closed shell, only use
1 for cases where the fragments have more than one unpaired spin each.

BOYSCALC

Specifies the Boys localized orbitals are to be calculated

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not perform localize the occupied space.
1
Allow core-valence mixing in Boys localization.
2
Localize core and valence separately.

RECOMMENDATION:

None

BOYS_CIS_NUMSTATE

Define how many states to mix with Boys localized diabatization. These states must be specified
in the *$localized_diabatization* section.

TYPE:

INTEGER

DEFAULT:

0
Do not perform Boys localized diabatization.

OPTIONS:

2 to N where N is the number of CIS states requested (CIS_N_ROOTS)

RECOMMENDATION:

It is usually not wise to mix adiabatic states that are separated by more than a few eV
or a typical reorganization energy in solvent.

CAGE_CHARGE

Defines the total charge of the cage.

TYPE:

INTEGER

DEFAULT:

400
Add a cage charged +4e.

OPTIONS:

$n$
Total charge of the cage is $n/100$ a.u.

RECOMMENDATION:

None

CAGE_POINTS

Defines number of point charges for the spherical cage.

TYPE:

INTEGER

DEFAULT:

100

OPTIONS:

$n$
Number of point charges to use.

RECOMMENDATION:

None

CAGE_RADIUS

Defines radius of the charged cage.

TYPE:

INTEGER

DEFAULT:

225

OPTIONS:

$n$
radius is $n/100$ Å.

RECOMMENDATION:

None

CALC_NAC

Whether or not non-adiabatic couplings
will be calculated for the EOM-CC, CIS, and TDDFT wave functions.

TYPE:

INTEGER

DEFAULT:

0 (do not compute NAC)

OPTIONS:

1
NYI for EOM-CC
2
Compute NACs using Szalay’s approach (this what needs to be specified for EOM-CC).

RECOMMENDATION:

Additional response equations will be solved and gradients for all EOM states and
for summed states will be computed,
which increases the cost of calculations.
Request only when needed and do not ask for too many EOM states.

CALC_SOC

Whether or not the spin-orbit couplings between CC/EOM/ADC/CIS/TDDFT electronic states
will be calculated. In the CC/EOM-CC suite, by default the couplings are calculated between
the CCSD reference and the EOM-CCSD target states. In order to calculate
couplings between EOM states, CC_STATE_TO_OPT must specify
the initial EOM state. If NTO analysis is requested, analysis of spinless transition density matrices
will be performed and the spin–orbit integrals over NTO pairs will be printed.

TYPE:

INTEGER/LOGICAL

DEFAULT:

FALSE (no spin-orbit couplings will be calculated)

OPTIONS:

0/FALSE
(no spin-orbit couplings will be calculated)
1/TRUE
Activates SOC calculation. EOM-CC/EOM-MP2 only: spin-orbit couplings will be computed with the new code with L+/L- averaging
2
EOM-CC/EOM-MP2 only: spin-orbit couplings will be computed with the new code without L+/L- averaging
3
EOM-CC/EOM-MP2 only: spin-orbit couplings will be computed with the legacy code

RECOMMENDATION:

CCMAN2 supports several variants of SOC calculation for EOM-CC/EOM-MP2 methods.
One-electron and mean-field two-electron SOCs will be computed by default.
To enable full two-electron SOCs, two-particle EOM properties must be
turned on (see CC_EOM_PROP_TE).

CALC_SOC

Controls whether to calculate the SOC constants for EOM-CC, RAS-CI, ADC, TDDFT/TDA and TDDFT.

TYPE:

INTEGER/LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not perform the SOC calculation.
TRUE
Perform the SOC calculation.

RECOMMENDATION:

Although TRUE/FALSE values will work, EOM-CC code has more variants of SOC evaluations. For details, consult with EOM section.

CAP_X_END

Controls the upper onset limit for a series of CAP onsets, where the lower limit is given
by CAP_X. The parameter value in a.u. is
obtained by multiplying the given integer by ${10}^{-3}$. Currently only used
in ADC methods.

TYPE:

INTEGER

DEFAULT:

CAP_X
Do not compute a series of CAP onsets but only use a single CAP with an
onset value of CAP_X.

OPTIONS:

$n>\text{CAP\_X}$
User-defined integer.

RECOMMENDATION:

Use this keyword if CAP onset series are desired.

CAP_X_STEP

Controls the step size for a series of CAP onsets between CAP_X and
CAP_X_END. The parameter value in a.u. is
obtained by multiplying the given integer by ${10}^{-3}$. Currently only used
in ADC methods.

TYPE:

INTEGER

DEFAULT:

500
corresponding to 0.5 a.u.

OPTIONS:

$n>0$
User-defined integer.

RECOMMENDATION:

None.

CAP_X

For ADC methods, in combination with a smoothed Voronoi-CAP
(CAP_TYPE = 2) or a spherical CAP (CAP_TYPE = 0),
this keyword controls the lower limit for a series of CAP onsets,
where the upper limit is given by CAP_X_END. The parameter value in a.u. is
obtained by multiplying the given integer by ${10}^{-3}$. In this case, the onset value defines the
region around the molecule with zero CAP strength. In combination with a
cuboid CAP (CAP_TYPE = 1) or in general for other electronic
structure methods (see 7.10.8 for further details), this keyword
controls the CAP onset in $x$ direction.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n>0$
User-defined integer.

RECOMMENDATION:

Usually, values of 2000 to 4000 (corresponding to onset values between 2.0 and 4.0 a.u.)
give reasonable results.

CAS_DAVIDSON_MAXVECTORS

Specifies the maximum number of vectors to augment the Davidson search space in CAS.

TYPE:

INTEGER

DEFAULT:

10

OPTIONS:

$N$
sets the maximum Davidson subspace size to $N$+CAS_N_ROOTS

RECOMMENDATION:

The default should be suitable in most cases

CAS_DAVIDSON_TOL

Specifies the tolerance for the Davidson solver used in CAS.

TYPE:

INTEGER

DEFAULT:

5

OPTIONS:

$N$
for a threshold of ${10}^{-N}$

RECOMMENDATION:

The default should be suitable in most cases

CAS_LOCAL_ALGO

Passed into localizer. Set to 1 if doing Boys localization.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$0$
No localization
$1$
Boys localization
$2$
Pipek-Mezey localization

RECOMMENDATION:

None.

CAS_LOCAL

Determines whether to do localization.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$0$
No localization
$1$
Boys localization
$2$
Pipek-Mezey localization

RECOMMENDATION:

None.

CAS_METHOD

Indicates whether orbital optimization is requested.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Not running a CAS calculation
1
CAS-CI (no orbital optimization)
2
CASSCF (orbital optimization)

RECOMMENDATION:

Use 2 for best accuracy, but such computations may become infeasible
for large active spaces.

CAS_M_S

The number of unpaired electrons desired in the CAS wavefunction.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$N$
for a wavefunction with $N$ unpaired electrons

RECOMMENDATION:

CAS_N_ELEC

Specifies the number of active electrons.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$N$
include $N$ electrons in the active space
-1
include all electrons in the active space

RECOMMENDATION:

Use the smallest active space possible for the given system.

CAS_N_ORB

Specifies the number of active orbitals.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$N$
include $N$ orbitals in the active space
-1
include all orbitals in the active space

RECOMMENDATION:

Use the smallest active space possible for the given system.

CAS_N_ROOTS

Specifies the number of electronic states to determine.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

$N$
solve for $N$ roots of the Hamiltonian

RECOMMENDATION:

CAS_SAVE_NAT_ORBS

Save the CAS natural orbitals in place of the reference orbitals.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
overwrite the reference orbitals with CAS natural orbitals
FALSE
do not save the CAS natural orbitals

RECOMMENDATION:

CAS_SOLVER

Specifies the solver to be used for the active space.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
CAS-CI/CASSCF
2
ASCI (see Section 6.21)
3
Truncated CI (CIS, CISD, CISDT, etc.)

RECOMMENDATION:

CAS_THRESH

Specifies the threshold for matrix elements to be included in the CAS Hamiltonian.

TYPE:

INTEGER

DEFAULT:

12

OPTIONS:

$N$
for a threshold of ${10}^{-N}$

RECOMMENDATION:

CAS_USE_RI

Indicates whether the resolution of the identity approximation should be used.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Compute 2-electron integrals analytically
TRUE
Use the RI approximation for 2-electron integrals

RECOMMENDATION:

Analytic integrals are more accurate, RI integrals are faster

CCVB_GUESS

Specifies the initial guess for CCVB calculations

TYPE:

INTEGER

DEFAULT:

NONE

OPTIONS:

1
Standard GVBMAN guess (orbital localization via GVB_LOCAL + Sano procedure).
2
Use orbitals from previous GVBMAN calculation, along with SCF_GUESS = READ.
3
Convert UHF orbitals into pairing VB form.

RECOMMENDATION:

Option 1 is the most useful overall. The success of GVBMAN methods is often
dependent on localized orbitals, and this guess shoots for these. Option 2 is
useful for comparing results to other GVBMAN methods, or if other GVBMAN
methods are able to obtain a desired result more efficiently. Option 3 can be
useful for bond-breaking situations when a pertinent UHF solution has been
found. It works best for small systems, or if the unrestriction is a local
phenomenon within a larger molecule. If the unrestriction is non-local and the
system is large, this guess will often produce a solution that is not the
global minimum. Any UHF solution has a certain number of pairs that are
unrestricted, and this will be output by the program. If GVB_N_PAIRS
exceeds this number, the standard GVBMAN initial-guess procedure will be used
to obtain a guess for the excess pairs

CCVB_METHOD

Optionally modifies the basic CCVB method

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
Standard CCVB model
3
Independent electron pair approximation (IEPA) to CCVB
4
Variational PP (the CCVB reference energy)

RECOMMENDATION:

Option 1 is generally recommended. Option 4 is useful for preconditioning, and
for obtaining localized-orbital solutions, which may be used in subsequent
calculations. It is also useful for cases in which the regular GVBMAN PP code
becomes variationally unstable. Option 3 is a simple independent-amplitude
approximation to CCVB. It avoids the cubic-scaling amplitude equations of CCVB,
and also is able to reach the correct dissociation energy for any molecular
system (unlike regular CCVB which does so only for cases in which UHF can reach
a correct dissociate limit). However the IEPA approximation to CCVB is
sometimes variationally unstable, which we have yet to observe in regular
CCVB.

CC_BACKEND

Used to specify the computational back-end of CCMAN2.

TYPE:

STRING

DEFAULT:

VM
Default shared-memory disk-based back-end

OPTIONS:

XM
libxm shared-memory disk-based back-end
INCORE
in-core memory back-end

RECOMMENDATION:

Use XM for large jobs with limited memory or when the performance of the
default disk-based back-end is not satisfactory, INCORE for small jobs that
fit in main memory.

CC_CANONIZE_FINAL

Whether to semi-canonicalize orbitals at the end of the ground state
calculation.

TYPE:

LOGICAL

DEFAULT:

FALSE
unless required

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

Should not normally have to be altered.

CC_CANONIZE_FREQ

The orbitals will be semi-canonicalized every $n$ theta resets. The thetas
(orbital rotation angles) are reset every CC_RESET_THETA
iterations. The counting of iterations differs for active space (VOD, VQCCD)
calculations, where the orbitals are always canonicalized at the first
theta-reset.

TYPE:

INTEGER

DEFAULT:

50

OPTIONS:

$n$
User-defined integer

RECOMMENDATION:

Smaller values can be tried in cases that do not converge.

CC_CANONIZE

Whether to semi-canonicalize orbitals at the start of the calculation (*i.e.*
Fock matrix is diagonalized in each orbital subspace)

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

Should not normally have to be altered.

CC_CONVERGENCE

Overall convergence criterion for the coupled-cluster codes. This is designed
to ensure at least $n$ significant digits in the calculated energy, and
automatically sets the other convergence-related variables
(CC_E_CONV, CC_T_CONV, CC_THETA_CONV,
CC_THETA_GRAD_CONV) [${10}^{-n}$].

TYPE:

INTEGER

DEFAULT:

6
Energies.
7
Gradients.

OPTIONS:

$n$
Corresponding to ${10}^{-n}$ convergence criterion. Amplitude convergence is set
automatically to match energy convergence.

RECOMMENDATION:

Use the default

CC_DIIS12_SWITCH

When to switch from DIIS2 to DIIS1 procedure, or when DIIS2 procedure is
required to generate DIIS guesses less frequently. Total value of DIIS error
vector must be less than ${10}^{-n}$, where $n$ is the value of this option.

TYPE:

INTEGER

DEFAULT:

5

OPTIONS:

$n$
User-defined integer

RECOMMENDATION:

None

CC_DIIS_FREQ

DIIS extrapolation will be attempted every n iterations. However, DIIS2 will
be attempted every iteration while total error vector exceeds
CC_DIIS12_SWITCH. DIIS1 cannot generate guesses more frequently than
every 2 iterations.

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

$N$
User-defined integer

RECOMMENDATION:

None

CC_DIIS_MAX_OVERLAP

DIIS extrapolations will not begin until square root of the maximum element of
the error overlap matrix drops below this value.

TYPE:

DOUBLE

DEFAULT:

100
Corresponding to 1.0

OPTIONS:

$abcde$
Integer code is mapped to $abc\times {10}^{-de}$

RECOMMENDATION:

None

CC_DIIS_MIN_OVERLAP

The DIIS procedure will be halted when the square root of smallest element of
the error overlap matrix is less than ${10}^{-n}$, where $n$ is the value of this
option. Small values of the B matrix mean it will become near-singular, making
the DIIS equations difficult to solve.

TYPE:

INTEGER

DEFAULT:

11

OPTIONS:

$n$
User-defined integer

RECOMMENDATION:

None

CC_DIIS_SIZE

Specifies the maximum size of the DIIS space.

TYPE:

INTEGER

DEFAULT:

7

OPTIONS:

$n$
User-defined integer

RECOMMENDATION:

Larger values involve larger amounts of disk storage.

CC_DIIS_START

Iteration number when DIIS is turned on. Set to a large number to disable
DIIS.

TYPE:

INTEGER

DEFAULT:

3

OPTIONS:

$n$
User-defined

RECOMMENDATION:

Occasionally DIIS can cause optimized orbital coupled-cluster calculations to
diverge through large orbital changes. If this is seen, DIIS should be
disabled.

CC_DIIS

Specify the version of Pulay’s Direct Inversion of the Iterative Subspace
(DIIS) convergence accelerator to be used in the coupled-cluster code.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Activates procedure 2 initially, and procedure 1 when gradients are smaller
than DIIS12_SWITCH.
1
Uses error vectors defined as differences between parameter vectors from
successive iterations. Most efficient near convergence.
2
Error vectors are defined as gradients scaled by square root of the
approximate diagonal Hessian. Most efficient far from convergence.

RECOMMENDATION:

DIIS1 can be more stable. If DIIS problems are encountered in the early stages
of a calculation (when gradients are large) try DIIS1.

CC_DIRECT_RI

Controls use of RI and Cholesky integrals in conventional (undecomposed) form

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
use all integrals in decomposed format
TRUE
transform all RI or Cholesky integral back to conventional format

RECOMMENDATION:

By default all integrals are used in decomposed format allowing significant
reduction of memory use. If all integrals are transformed back (TRUE option) no
memory reduction is achieved and decomposition error is introduced, however,
the integral transformation is performed significantly faster and conventional
CC/EOM algorithms are used.

CC_DOV_THRESH

Specifies minimum allowed values for the coupled-cluster energy denominators.
Smaller values are replaced by this constant during early iterations only, so
the final results are unaffected, but initial convergence is improved when the
HOMO-LUMO gap is small or when non-conventional references are used.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$abcde$
Integer code is mapped to $ab\times {10}^{-de}$, *e.g.*,
$2501$ corresponds to 0.025, $99001$ corresponds to 0.99, etc.

RECOMMENDATION:

Increase to 0.25, 0.5 or 0.75 for non convergent coupled-cluster calculations.

CC_DO_DYSON_EE

Whether excited-state or spin-flip state Dyson orbitals will be calculated for
EOM-IP/EA-CCSD calculations with CCMAN.

TYPE:

LOGICAL

DEFAULT:

FALSE (the option must be specified to run this calculation)

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

none

CC_DO_DYSON

CCMAN2: starts all types of Dyson orbitals calculations. Desired type is
determined by requesting corresponding EOM-XX transitions
CCMAN: whether the reference-state Dyson orbitals will be calculated for
EOM-IP/EA-CCSD calculations.

TYPE:

LOGICAL

DEFAULT:

FALSE (the option must be specified to run this calculation)

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

none

CC_DO_FESHBACH

Activates calculation of resonance widths using Feshbach-Fano approach.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
do not invoke Feshbach-Fano calculation
1
invoke Feshbach-Fano calculation of the resonance width
2
invoke Feshbach-Fano calculation of the resonance width and resonance shift

RECOMMENDATION:

Initial and final states should be correctly specified.

CC_EOM_2PA

Whether or not the transition moments and cross-sections for two-photon
absorption will be calculated. By default, the
transition moments are calculated between the CCSD reference and the
EOM-CCSD target states. In order to calculate transition moments between
a set of EOM-CCSD states and another EOM-CCSD state, the
CC_STATE_TO_OPT must be specified for this state.
If 2PA NTO analysis is requested, the CC_EOM_2PA value is redundant
as long as CC_EOM_2PA $>0$.

TYPE:

INTEGER

DEFAULT:

0 (do not compute 2PA transition moments)

OPTIONS:

1
Compute 2PA using the fastest algorithm (use $\stackrel{~}{\sigma}$-intermediates for
canonical
and $\sigma $-intermediates for RI/CD response calculations).
2
Use $\sigma $-intermediates for 2PA response equation calculations.
3
Use $\stackrel{~}{\sigma}$-intermediates for 2PA response equation calculations.

RECOMMENDATION:

Additional response equations (6 for each target state) will be solved,
which increases the cost of calculations. The cost of 2PA
moments is about 10 times that of energy calculation.
Use the default algorithm.
Setting CC_EOM_2PA $>0$ turns on CC_TRANS_PROP.

CC_EOM_PROP_TE

Request for calculation of non-relaxed two-particle EOM-CC properties. The
two-particle properties currently include $\u27e8{S}^{2}\u27e9$. The one-particle
properties also will be calculated, since the additional cost of the
one-particle properties calculation is inferior compared to the cost of
$\u27e8{S}^{2}\u27e9$. The variable CC_EOM_PROP must be also set to
TRUE. Alternatively, CC_CALC_SSQ can be used to
request $\u27e8{S}^{2}\u27e9$ calculation.

TYPE:

LOGICAL

DEFAULT:

FALSE
(no two-particle properties will be calculated)

OPTIONS:

FALSE, TRUE

RECOMMENDATION:

The two-particle properties are computationally expensive since
they require calculation and use of the two-particle density matrix (the cost
is approximately the same as the cost of an analytic gradient calculation). Do
not request the two-particle properties unless you really need them.

CC_EOM_PROP

Whether or not the non-relaxed (expectation value) one-particle EOM-CCSD
target state properties will be calculated. The properties currently include
permanent dipole moment, angular momentum projections, the second moments $\u27e8{X}^{2}\u27e9$, $\u27e8{Y}^{2}\u27e9$, and
$\u27e8{Z}^{2}\u27e9$ of electron density, and the total $\u27e8{R}^{2}\u27e9=\u27e8{X}^{2}\u27e9+\u27e8{Y}^{2}\u27e9+\u27e8{Z}^{2}\u27e9$ (in atomic units). Incompatible with
JOBTYPE = FORCE, OPT, FREQ.

TYPE:

LOGICAL

DEFAULT:

FALSE (no one-particle properties will be calculated)

OPTIONS:

FALSE, TRUE

RECOMMENDATION:

Additional equations (EOM-CCSD equations for the left eigenvectors) need to be
solved for properties, approximately doubling the cost of calculation for each
irrep.
The cost of the one-particle properties calculation itself is low. The
one-particle density of an EOM-CCSD target state can be analyzed with NBO or
libwfa packages by specifying the state with CC_STATE_TO_OPT and
requesting NBO = TRUE and CC_EOM_PROP = TRUE.

CC_EOM_RIXS

Whether or not the RIXS scattering moments and cross-sections will be calculated.

TYPE:

INTEGER

DEFAULT:

0
do not compute RIXS cross-sections

OPTIONS:

1
Perform RIXS within fc-CVS-EOM-EE-CCSD using the response wave functions of the CCSD reference state only
2
Perform RIXS within fc-CVS-EOM-EE-CCSD response theory along with the wave-function analysis of RIXS transition density matrices
11
Perform RIXS within the standard EOM-EE-CCSD using the response wave functions of the CCSD reference state only
12
Use $\sigma $-intermediates for RIXS response calculations within the standard EOM-EE-CCSD

RECOMMENDATION:

Use 1 to deploy fc-CVS-EOM-EE-CCSD with robust convergence

CC_ERASE_DP_INTEGRALS

Controls storage of requisite objects computed with double precision in a single-precision calculation

TYPE:

INTEGER

DEFAULT:

0
store

OPTIONS:

1
do not store

RECOMMENDATION:

Do not erase integrals if clean-up in double precision is intended.

CC_E_CONV

Convergence desired on the change in total energy, between iterations.

TYPE:

INTEGER

DEFAULT:

10

OPTIONS:

$n$
${10}^{-n}$ convergence criterion.

RECOMMENDATION:

None

CC_FESHBACH_CW

Activates Coulomb wave description of the ejected electron.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Use plane wave
1
Use Coulomb wave

RECOMMENDATION:

Additional details need to be specified in *$coulomb_wave* section.

CC_FESHBACH_DELTA_INTB

Specifies integration limits in calculation of energy shift in Feshbach-Fano calculations.

TYPE:

INTEGER

DEFAULT:

Preset

OPTIONS:

$n$
corresponds to energy limit in eV

RECOMMENDATION:

Use default.

CC_FESHBACH_DELTA_INTC

Specifies integration limits in calculation of energy shift in Feshbach-Fano calculations.

TYPE:

INTEGER

DEFAULT:

Preset

OPTIONS:

$n$
corresponds to energy limit in eV

RECOMMENDATION:

Use default.

CC_FNO_THRESH

Initialize the FNO truncation and sets the threshold to be used for both
cutoffs (OCCT and POVO)

TYPE:

INTEGER

DEFAULT:

None

OPTIONS:

range
0000-10000
$abcd$
Corresponding to $ab.cd$%

RECOMMENDATION:

None

CC_FNO_USEPOP

Selection of the truncation scheme

TYPE:

INTEGER

DEFAULT:

1
OCCT

OPTIONS:

0
POVO

RECOMMENDATION:

None

CC_FULLRESPONSE

Fully relaxed properties (including orbital relaxation terms) will be computed.
The variable CC_REF_PROP must be also set to TRUE.

TYPE:

LOGICAL

DEFAULT:

FALSE
(no orbital response will be calculated)

OPTIONS:

FALSE, TRUE

RECOMMENDATION:

Not available for non UHF/RHF references and for the methods that do not have
analytic gradients (*e.g.*, QCISD).

CC_HESS_THRESH

Minimum allowed value for the orbital Hessian. Smaller values are replaced by
this constant.

TYPE:

DOUBLE

DEFAULT:

102
Corresponding to 0.01

OPTIONS:

$abcde$
Integer code is mapped to $abc\times {10}^{-de}$

RECOMMENDATION:

None

CC_INCL_CORE_CORR

Whether to include the correlation contribution from frozen core orbitals in
non iterative (2) corrections, such as OD(2) and CCSD(2).

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
FALSE

RECOMMENDATION:

Use the default unless no core-valence or core correlation is desired (*e.g.*, for
comparison with other methods or because the basis used cannot describe core
correlation).

CC_ITERATE_ON

In active space calculations, use a “mixed” iteration procedure if the
value is greater than 0. Then if the RMS orbital gradient is larger than the
value of CC_THETA_GRAD_THRESH, micro-iterations will be performed
to converge the occupied-virtual mixing angles for the current active space.
The maximum number of space iterations is given by this option.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Up to $n$ occupied-virtual iterations per overall cycle

RECOMMENDATION:

Can be useful for non-convergent active space calculations

CC_ITERATE_OV

In active space calculations, use a “mixed” iteration procedure if the value
is greater than 0. Then, if the RMS orbital gradient is larger than the value
of CC_THETA_GRAD_THRESH, micro-iterations will be performed to
converge the occupied-virtual mixing angles for the current active space. The
maximum number of such iterations is given by this option.

TYPE:

INTEGER

DEFAULT:

0
No “mixed” iterations

OPTIONS:

$n$
Up to $n$ occupied-virtual iterations per overall cycle

RECOMMENDATION:

Can be useful for non-convergent active space calculations.

CC_MAX_ITER

Maximum number of iterations to optimize the coupled-cluster energy.

TYPE:

INTEGER

DEFAULT:

200

OPTIONS:

$n$
up to $n$ iterations to achieve convergence.

RECOMMENDATION:

None

CC_MEMORY

Specifies the maximum size, in MB, of the buffers for in-core storage of
block-tensors in CCMAN and CCMAN2.

TYPE:

INTEGER

DEFAULT:

50% of MEM_TOTAL. If MEM_TOTAL is not set, use 1.5 GB.
A minimum of
192 MB is hard-coded.

OPTIONS:

$n$
Integer number of MB

RECOMMENDATION:

Larger values can give better I/O performance and are recommended for systems
with large memory (add to your .qchemrc file. When running
CCMAN2 exclusively on a node, CC_MEMORY should be set to
75–80% of the total available RAM. )

CC_MP2NO_GRAD

If CC_MP2NO_GUESS is TRUE, what kind of one-particle
density matrix is used to make the guess orbitals?

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
1 PDM from MP2 gradient theory.
FALSE
1 PDM expanded to 2${}^{\mathrm{nd}}$ order in perturbation theory.

RECOMMENDATION:

The two definitions give generally similar performance.

CC_MP2NO_GUESS

Will guess orbitals be natural orbitals of the MP2 wave function?
Alternatively, it is possible to use an effective one-particle density matrix
to define the natural orbitals.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Use natural orbitals from an MP2 one-particle density matrix (see
*CC_MP2NO_GRAD*).
FALSE
Use current molecular orbitals from SCF.

RECOMMENDATION:

None

CC_ORBS_PER_BLOCK

Specifies target (and maximum) size of blocks in orbital space.

TYPE:

INTEGER

DEFAULT:

16

OPTIONS:

$n$
Orbital block size of $n$ orbitals.

RECOMMENDATION:

None

CC_OSFNO

Activation of OSFNO. Available only for open-shell references.

TYPE:

LOGICAL

DEFAULT:

FALSE
do not activate

OPTIONS:

TRUE
activate

RECOMMENDATION:

Use for EOM-SF-CCSD calculations from open-shell references. Available in CCMAN2 only.

CC_POL

Specifies the approach for calculating the polarizability of the CCSD wave function.

TYPE:

INTEGER

DEFAULT:

0
(CCSD polarizability will not be calculated)

OPTIONS:

1
(analytic-derivative or response-theory mixed symmetric-asymmetric approach)
2
(analytic-derivative or response-theory asymmetric approach)
3
(expectation-value approach with right response intermediates)
4
(expectation-value approach with left response intermediates)

RECOMMENDATION:

CCSD polarizabilities are expensive since they require solving
three/six (for static) or six/twelve (for dynamical)
additional response equations. Do no request this property unless you need it.

CC_PRECONV_FZ

In active space methods, whether to pre-converge other wave function variables
for fixed initial guess of active space.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
No pre-iterations before active space optimization begins.
$n$
Maximum number of pre-iterations via this procedure.

RECOMMENDATION:

None

CC_PRECONV_T2Z_EACH

Whether to pre-converge the cluster amplitudes before each change of the
orbitals in optimized orbital coupled-cluster methods. The maximum number of
iterations in this pre-convergence procedure is given by the value of this
parameter.

TYPE:

INTEGER

DEFAULT:

0
(FALSE)

OPTIONS:

0
No pre-convergence before orbital optimization.
$n$
Up to $n$ iterations in this pre-convergence procedure.

RECOMMENDATION:

A very slow last resort option for jobs that do not converge.

CC_PRECONV_T2Z

Whether to pre-converge the cluster amplitudes before beginning orbital
optimization in optimized orbital cluster methods.

TYPE:

INTEGER

DEFAULT:

0
(FALSE)
10
If CC_RESTART, CC_RESTART_NO_SCF or
CC_MP2NO_GUESS are TRUE

OPTIONS:

0
No pre-convergence before orbital optimization.
$n$
Up to $n$ iterations in this pre-convergence procedure.

RECOMMENDATION:

Experiment with this option in cases of convergence failure.

CC_PRINT

Controls the output from post-MP2 coupled-cluster module of Q-Chem

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

$0-7$
higher values can lead to deforestation…

RECOMMENDATION:

Increase if you need more output and don’t like trees

CC_QCCD_THETA_SWITCH

QCCD calculations switch from OD to QCCD when the rotation gradient is below
this threshold [${10}^{-n}$]

TYPE:

INTEGER

DEFAULT:

2
${10}^{-2}$ switchover

OPTIONS:

$n$
${10}^{-n}$ switchover

RECOMMENDATION:

None

CC_REF_PROP_TE

Request for calculation of non-relaxed two-particle CCSD properties. The
two-particle properties currently include $\u27e8{S}^{2}\u27e9$. The one-particle
properties also will be calculated, since the additional cost of the
one-particle properties calculation is inferior compared to the cost of
$\u27e8{S}^{2}\u27e9$. The variable CC_REF_PROP must be also set to
TRUE.

TYPE:

LOGICAL

DEFAULT:

FALSE
(no two-particle properties will be calculated)

OPTIONS:

FALSE, TRUE

RECOMMENDATION:

The two-particle properties are computationally expensive, since
they require calculation and use of the two-particle density matrix (the cost
is approximately the same as the cost of an analytic gradient calculation). Do
not request the two-particle properties unless you really need them.

CC_REF_PROP

Whether or not the non-relaxed (expectation value) or full response (including
orbital relaxation terms) one-particle CCSD
properties will be calculated. The properties currently include permanent
dipole moment, the second moments $\u27e8{X}^{2}\u27e9$, $\u27e8{Y}^{2}\u27e9$, and
$\u27e8{Z}^{2}\u27e9$ of electron density, and the total
$\u27e8{R}^{2}\u27e9=\u27e8{X}^{2}\u27e9+\u27e8{Y}^{2}\u27e9+\u27e8{Z}^{2}\u27e9$ (in atomic units).
Incompatible with JOBTYPE = FORCE, OPT, or FREQ.

TYPE:

LOGICAL

DEFAULT:

FALSE
(no one-particle properties will be calculated)

OPTIONS:

FALSE, TRUE

RECOMMENDATION:

Additional equations need to be solved (lambda CCSD equations) for properties
with the cost approximately the same as CCSD equations. Use the default if you do
not need properties. The cost of the properties calculation itself is low. The
CCSD one-particle density can be analyzed with NBO package by specifying
NBO = TRUE, CC_REF_PROP = TRUE, and i
JOBTYPE = FORCE.

CC_RESET_THETA

The reference MO coefficient matrix is reset every n iterations to help
overcome problems associated with the theta metric as theta becomes large.

TYPE:

INTEGER

DEFAULT:

15

OPTIONS:

$n$
$n$ iterations between resetting orbital rotations to zero.

RECOMMENDATION:

None

CC_RESTART_NO_SCF

Should an optimized orbital coupled cluster calculation begin with optimized
orbitals from a previous calculation? When TRUE, molecular orbitals are
initially orthogonalized, and CC_PRECONV_T2Z and
CC_CANONIZE are set to TRUE while other guess options are set to
FALSE

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

None

CC_RESTART

Allows an optimized orbital coupled cluster calculation to begin with an
initial guess for the orbital transformation matrix U other than the unit
vector. The scratch file from a previous run must be available for the U
matrix to be read successfully.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Use unit initial guess.
TRUE
Activates CC_PRECONV_T2Z, CC_CANONIZE, and
turns off CC_MP2NO_GUESS

RECOMMENDATION:

Useful for restarting a job that did not converge, if files were saved.

CC_RESTR_AMPL

Controls the restriction on amplitudes is there are restricted orbitals

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

0
All amplitudes are in the full space
1
Amplitudes are restricted, if there are restricted orbitals

RECOMMENDATION:

None

CC_RESTR_TRIPLES

Controls which space the triples correction is computed in

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Triples are computed in the full space
1
Triples are restricted to the active space

RECOMMENDATION:

None

CC_REST_AMPL

Forces the integrals, $T$, and $R$ amplitudes to be determined in the full
space even though the CC_REST_OCC and CC_REST_VIR
keywords are used.

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

FALSE
Do apply restrictions
TRUE
Do not apply restrictions

RECOMMENDATION:

None

CC_REST_OCC

Sets the number of restricted occupied orbitals including active core occupied
orbitals.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Restrict $n$ energetically lowest occupied orbitals to correspond to the
active core space.

RECOMMENDATION:

*Example:* cytosine with the molecular formula C${}_{4}$H${}_{5}$N${}_{3}$O
includes one oxygen atom. To calculate O 1s core-excited states, $n$ has to be
set to 1, because the 1s orbital of oxygen is the energetically lowest. To
obtain the N 1s core excitations, the integer $n$ has to be set to 4, because
the 1s orbital of the oxygen atom is included as well, since it is
energetically below the three 1s orbitals of the nitrogen atoms. Accordingly,
to simulate the C 1s spectrum of cytosine, $n$ must be set to 8.

CC_REST_TRIPLES

Restricts ${R}_{3}$ amplitudes to the active space, *i.e.*, one electron should be
removed from the active occupied orbital and one electron should be added to
the active virtual orbital.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
Applies the restrictions

RECOMMENDATION:

None

CC_REST_VIR

Sets the number of restricted virtual orbitals including frozen virtual
orbitals.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Restrict $n$ virtual orbitals.

RECOMMENDATION:

None

CC_SCALE_AMP

If not 0, scales down the step for updating coupled-cluster amplitudes in cases of problematic convergence.

TYPE:

INTEGER

DEFAULT:

0
no scaling

OPTIONS:

$abcd$
Integer code is mapped to $abcd\times {10}^{-2}$, *e.g.*,
$90$ corresponds to 0.9

RECOMMENDATION:

Use 0.9 or 0.8 for non convergent coupled-cluster calculations.

CC_SINGLE_PREC

Precision selection for CCSD calculation. Available in CCMAN2 only.

TYPE:

INTEGER

DEFAULT:

0
double-precision calculation

OPTIONS:

1
single-precision calculation
2
single-precision calculation followed by double-precision clean-up iterations

RECOMMENDATION:

Do not set too tight convergence thresholds when using single precision

CC_SP_DM

Precision selection for CCSD and EOM-CCSD intermediates, density matrices, gradients, and ${S}^{2}$

TYPE:

INTEGER

DEFAULT:

0
double-precision calculation

OPTIONS:

1
single-precision calculation

RECOMMENDATION:

NONE

CC_SP_E_CONV

Energy convergence criterion in single precision in CCSD calculations.

TYPE:

INTEGER

DEFAULT:

5

OPTIONS:

$n$
Corresponding to ${10}^{-n}$ convergence criterion

RECOMMENDATION:

Set 6 to be consistent with the default threshold in double precision in a pure
single-precision calculation.
When used with clean-up version, it should be smaller than double-precision
threshold not to introduce extra iterations.

CC_SP_T_CONV

Amplitude convergence threshold in single precision in CCSD calculations.

TYPE:

INTEGER

DEFAULT:

3

OPTIONS:

$n$
Corresponding to ${10}^{-n}$ convergence criterion

RECOMMENDATION:

Set 4 to be consistent with the default threshold in double precision in a pure
single-precision run. When used with clean-up version, it should be smaller
than double-precision threshold not to introduce extra iterations.

CC_STATE_TO_OPT

Specifies which state to optimize.

TYPE:

INTEGER ARRAY

DEFAULT:

None

OPTIONS:

[$i$,$j$]
optimize the $j$th state of the $i$th irrep.

RECOMMENDATION:

None

CC_SYMMETRY

Activates point-group symmetry in the ADC calculation.

TYPE:

LOGICAL

DEFAULT:

TRUE
If the system possesses any point-group symmetry.

OPTIONS:

TRUE
Employ point-group symmetry
FALSE
Do not use point-group symmetry

RECOMMENDATION:

None

CC_THETA_CONV

Convergence criterion on the RMS difference between successive sets of
orbital rotation angles [${10}^{-n}$].

TYPE:

INTEGER

DEFAULT:

5
Energies
6
Gradients

OPTIONS:

$n$
${10}^{-n}$ convergence criterion.

RECOMMENDATION:

Use default

CC_THETA_GRAD_CONV

Convergence desired on the RMS gradient of the energy with respect to
orbital rotation angles [${10}^{-n}$].

TYPE:

INTEGER

DEFAULT:

7
Energies
8
Gradients

OPTIONS:

$n$
${10}^{-n}$ convergence criterion.

RECOMMENDATION:

Use default

CC_THETA_GRAD_THRESH

RMS orbital gradient threshold [${10}^{-n}$] above which “mixed iterations”
are performed in active space calculations if CC_ITERATE_OV is
TRUE.

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

$n$
${10}^{-n}$ threshold.

RECOMMENDATION:

Can be made smaller if convergence difficulties are encountered.

CC_THETA_STEPSIZE

Scale factor for the orbital rotation step size. The optimal rotation steps
should be approximately equal to the gradient vector.

TYPE:

INTEGER

DEFAULT:

$100$
Corresponding to 1.0

OPTIONS:

$abcde$
Integer code is mapped to $abc\times {10}^{-de}$
If the initial step is smaller than 0.5, the program will increase step
when gradients are smaller than the value of THETA_GRAD_THRESH,
up to a limit of 0.5.

RECOMMENDATION:

Try a smaller value in cases of poor convergence and very large orbital
gradients. For example, a value of 01001 translates to 0.1

CC_TRANS_PROP

Whether or not the transition dipole moment (in atomic units) and oscillator
strength and rotatory strength (in atomic units)
for the EOM-CCSD target states will be calculated. By default, the
transition dipole moment, angular momentum matrix elements,
and rotatory strengths
are calculated between the CCSD reference and the
EOM-CCSD target states. In order to calculate transition dipole moment, angular momentum matrix elements,
and rotatory strengths between a set of EOM-CCSD states and another EOM-CCSD state, the
CC_STATE_TO_OPT
must be specified for this state.

TYPE:

INTEGER

DEFAULT:

0 (no transition properties will be calculated)

OPTIONS:

1 (calculate transition properties between all computed EOM state and the reference state)
2 (calculate transition properties between all pairs of EOM states)

RECOMMENDATION:

Additional equations (for the left EOM-CCSD eigenvectors plus lambda CCSD
equations in case of transition properties between the CCSD reference and
EOM-CCSD target states are requested) need to be solved for transition
properties, approximately doubling the computational cost. The cost of the
transition properties calculation itself is low.

CC_T_CONV

Convergence criterion on the RMS difference between successive sets of
coupled-cluster doubles amplitudes [${10}^{-n}$]

TYPE:

INTEGER

DEFAULT:

8
energies
10
gradients

OPTIONS:

$n$
${10}^{-n}$ convergence criterion.

RECOMMENDATION:

Use default

CC_Z_CONV

Convergence criterion on the RMS difference between successive doubles
$Z$-vector amplitudes [${10}^{-n}$].

TYPE:

INTEGER

DEFAULT:

8
Energies
10
Gradients

OPTIONS:

$n$
${10}^{-n}$ convergence criterion.

RECOMMENDATION:

Use Default

CDFTCI_PRINT

Controls level of output from CDFT-CI procedure to Q-Chem output file.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Only print energies and coefficients of CDFT-CI final states
1
Level 0 plus CDFT-CI overlap, Hamiltonian, and population matrices
2
Level 1 plus eigenvectors and eigenvalues of the CDFT-CI population matrix
3
Level 2 plus promolecule orbital coefficients and energies

RECOMMENDATION:

Level 3 is primarily for program debugging; levels 1 and 2 may be useful
for analyzing the coupling elements

CDFTCI_RESTART

To be used in conjunction with CDFTCI_STOP, this variable
causes CDFT-CI to read already-converged states from disk and begin
SCF convergence on later states. Note that the same *$cdft* section
must be used for the stopped calculation and the restarted calculation.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Start calculations on state $n+1$

RECOMMENDATION:

Use this setting in conjunction with CDFTCI_STOP.

CDFTCI_SKIP_PROMOLECULES

Skips promolecule calculations and allows fractional charge and spin
constraints to be specified directly.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Standard CDFT-CI calculation is performed.
TRUE
Use the given charge/spin constraints directly, with no
promolecule calculations.

RECOMMENDATION:

Setting to TRUE can be useful for scanning over constraint values.

CDFTCI_STOP

The CDFT-CI procedure involves performing independent SCF calculations on
distinct constrained states. It sometimes occurs that the same convergence
parameters are not successful for all of the states of interest, so that a
CDFT-CI calculation might converge one of these diabatic states but not the
next. This variable allows a user to stop a CDFT-CI calculation after a
certain number of states have been converged, with the ability to restart later
on the next state, with different convergence options.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Stop after converging state $n$ (the first state is state $1$)
$0$
Do not stop early

RECOMMENDATION:

Use this setting if some diabatic states converge but others do not.

CDFTCI_SVD_THRESH

By default, a symmetric orthogonalization is performed on the CDFT-CI
matrix before diagonalization. If the CDFT-CI overlap matrix is nearly
singular (*i.e.*, some of the diabatic states are nearly degenerate), then
this orthogonalization can lead to numerical instability. When computing
${\mathbf{S}}^{-1/2}$, eigenvalues smaller than ${10}^{-\mathrm{CDFTCI}\mathrm{\_}\mathrm{SVD}\mathrm{\_}\mathrm{THRESH}}$
are discarded.

TYPE:

INTEGER

DEFAULT:

4

OPTIONS:

$n$
for a threshold of ${10}^{-n}$.

RECOMMENDATION:

Can be decreased if numerical instabilities are encountered in the
final diagonalization.

CDFTCI

Initiates a constrained DFT-configuration interaction calculation

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform a CDFT-CI Calculation
FALSE
No CDFT-CI

RECOMMENDATION:

Set to TRUE if a CDFT-CI calculation is desired.

CDFT_BECKE_POP

Whether the calculation should print the Becke atomic charges at convergence

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
Print Populations
FALSE
Do not print them

RECOMMENDATION:

Use the default. Note that the Mulliken populations printed at the end of an
SCF run will not typically add up to the prescribed constraint value. Only the
Becke populations are guaranteed to satisfy the user-specified constraints.

CDFT_LAMBDA_MODE

Allows CDFT potentials to be specified directly, instead of being
determined as Lagrange multipliers.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Standard CDFT calculations are used.
TRUE
Instead of specifying target charge and spin constraints, use the values
from the input deck as the value of the Becke weight potential

RECOMMENDATION:

Should usually be set to FALSE. Setting to TRUE can be useful to scan over
different strengths of charge or spin localization, as convergence properties
are improved compared to regular CDFT(-CI) calculations.

CDFT_MAXITER

Maximum number of iterations for converging the constraint.

TYPE:

INTEGER

DEFAULT:

20

OPTIONS:

N
A maximum of N microiterations will be attempted.

RECOMMENDATION:

Default value is expected to be sufficient in most situations.

CDFT_POP

Sets the charge partitioning scheme for cDFT or cDFT-CI jobs.

TYPE:

STRING

DEFAULT:

BECKE

OPTIONS:

BECKE
Linear combination of atomic Becke functions
FBH
Fragment-based Hirshfeld partition

RECOMMENDATION:

None

CDFT_POSTDIIS

Controls whether the constraint is enforced after DIIS extrapolation.

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
Enforce constraint after DIIS
FALSE
Do not enforce constraint after DIIS

RECOMMENDATION:

Use the default unless convergence problems arise,
in which case it may be beneficial to experiment with setting CDFT_POSTDIIS
to FALSE.
With this option set to TRUE, energies should be variational after the first iteration.

CDFT_PREDIIS

Controls whether the constraint is enforced before DIIS extrapolation.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Enforce constraint before DIIS
FALSE
Do not enforce constraint before DIIS

RECOMMENDATION:

Use the default unless convergence problems arise, in which case it may be beneficial to experiment with setting
CDFT_PREDIIS to TRUE. Note that it is possible to enforce the constraint
both before and after DIIS by setting both CDFT_PREDIIS and CDFT_POSTDIIS
to TRUE.

CDFT_PRINT

Whether detailed information about CDFT iterations should be printed in the output file.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Print detailed information.
FALSE
Do not print detailed information.

RECOMMENDATION:

Use the default and invoke additional printing for troubleshooting.

CDFT_THRESH

Threshold that determines how tightly the constraint must be satisfied.

TYPE:

INTEGER

DEFAULT:

5

OPTIONS:

N
Constraint is satisfied to within ${10}^{-N}$.

RECOMMENDATION:

Default value is set to match SCF_CONVERGENCE. Use the default unless problems occur.

CDFT

Initiates a constrained DFT calculation

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform a Constrained DFT Calculation
FALSE
No Density Constraint

RECOMMENDATION:

Set to TRUE if a Constrained DFT calculation is desired.

CD_ALGORITHM

Determines the algorithm for MP2 integral transformations.

TYPE:

STRING

DEFAULT:

Program determined.

OPTIONS:

DIRECT
Uses fully direct algorithm (energies only).
SEMI_DIRECT
Uses disk-based semi-direct algorithm.
LOCAL_OCCUPIED
Alternative energy algorithm (see 6.4.1).

RECOMMENDATION:

Semi-direct is usually most efficient, and will normally be chosen by default.

CFMM_ORDER

Controls the order of the multipole expansions in CFMM calculation.

TYPE:

INTEGER

DEFAULT:

15
For single point SCF accuracy
25
For tighter convergence (optimizations)

OPTIONS:

$n$
Use multipole expansions of order $n$

RECOMMENDATION:

Use the default.

CHARGE_CHARGE_REPULSION

The repulsive Coulomb interaction parameter for YinYang atoms.

TYPE:

INTEGER

DEFAULT:

550

OPTIONS:

$n$
Use Q = $n\times {10}^{-3}$

RECOMMENDATION:

The repulsive Coulomb potential maintains bond lengths involving YinYang
atoms with the potential $V(r)=Q/r$. The default is parameterized for carbon atoms.

CHELPG_DX

Sets the rectangular grid spacing for the traditional Cartesian ChElPG grid or
the spacing between concentric Lebedev shells (when the variables CHELPG_HA
and CHELPG_H are specified as well).

TYPE:

INTEGER

DEFAULT:

6

OPTIONS:

$N$
Corresponding to a grid space of $N/20$, in Å.

RECOMMENDATION:

Use the default, which corresponds to the “dense grid” of Breneman and
Wiberg,
^{
130
}
J. Comput. Chem.

(1990),
11,
pp. 361.
Link
, unless the cost is prohibitive, in which case a
larger value can be selected. Note that this default value is set with the
Cartesian grid in mind and not the Lebedev grid. In the Lebedev case, a larger
value can typically be used.

CHELPG_HA

Sets the Lebedev grid to use for non-hydrogen atoms.

TYPE:

INTEGER

DEFAULT:

NONE

OPTIONS:

$N$
Corresponding to a number of points in a Lebedev grid (see Section 5.5.1.

RECOMMENDATION:

None.

CHELPG_HEAD

Sets the “head space”
^{
130
}
J. Comput. Chem.

(1990),
11,
pp. 361.
Link
(radial extent) of the ChElPG grid.

TYPE:

INTEGER

DEFAULT:

30

OPTIONS:

$N$
Corresponding to a head space of $N/10$, in Å.

RECOMMENDATION:

Use the default, which is the value recommended by Breneman and Wiberg.
^{
130
}
J. Comput. Chem.

(1990),
11,
pp. 361.
Link

CHELPG_H

Sets the Lebedev grid to use for hydrogen atoms.

TYPE:

INTEGER

DEFAULT:

NONE

OPTIONS:

$N$
Corresponding to a number of points in a Lebedev grid.

RECOMMENDATION:

CHELPG_H must always be less than or equal to CHELPG_HA. If it is greater,
it will automatically be set to the value of CHELPG_HA.

CHELPG

Controls the calculation of CHELPG charges.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not calculate ChElPG charges.
TRUE
Compute ChElPG charges.

RECOMMENDATION:

Set to TRUE if desired. For large molecules, there is some overhead
associated with computing
ChElPG charges, especially if the number of grid points is large.

CHILD_MP_ORDERS

The multipole orders included in the prepared FERFs. The last digit specifies how many multipoles to compute,
and the digits in the front specify the multipole orders: 2: dipole (D); 3: quadrupole (Q); 4: octopole (O). Multipole
order 1 is reserved for monopole FERFs which can be used to separate the effect of orbital contraction.
^{
655
}
J. Phys. Chem. Lett.

(2017),
8,
pp. 1967.
Link

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

21
D
232
DQ
2343
DQO

RECOMMENDATION:

Use 232 (DQ) when FERF is needed.

CHILD_MP

Compute FERFs for fragments and use them as the basis for SCFMI calculations.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not compute FERFs (use the full AO span of each fragment).
TRUE
Compute fragment FERFs.

RECOMMENDATION:

Use FERFs to compute polarization energy when large basis sets are used. In an “EDA2" calculation,
this *$rem* variable is set based on the given option automatically.

CHOLESKY_TOL

Tolerance of Cholesky decomposition of two-electron integrals

TYPE:

INTEGER

DEFAULT:

3

OPTIONS:

$n$
Corresponds to a tolerance of ${10}^{-n}$

RECOMMENDATION:

2 - qualitative calculations, 3 - appropriate for most cases, 4 - quantitative
(error in total energy typically less than 1 $\mu $hartree)

CISTR_PRINT

Controls level of output.

TYPE:

LOGICAL

DEFAULT:

FALSE
Minimal output.

OPTIONS:

TRUE
Increase output level.

RECOMMENDATION:

None

CIS_AMPL_ANAL

Perform additional analysis of CIS and TDDFT excitation amplitudes,
including generation of natural transition orbitals, excited-state
multipole moments, and Mulliken analysis of the excited state densities
and particle/hole density matrices.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform additional amplitude analysis.
FALSE
Do not perform additional analysis.

RECOMMENDATION:

None

CIS_AMPL_PRINT

Sets the threshold for printing CIS and TDDFT excitation amplitudes.

TYPE:

INTEGER

DEFAULT:

15

OPTIONS:

$n$
Print if $|{x}_{ia}|$ or $|{y}_{ia}|$ is larger than $0.1\times n$.

RECOMMENDATION:

Use the default unless you want to see more amplitudes.

CIS_CONVERGENCE

CIS is considered converged when error is less than ${10}^{-\mathrm{CIS}\mathrm{\_}\mathrm{CONVERGENCE}}$

TYPE:

INTEGER

DEFAULT:

6
CIS convergence threshold 10${}^{-6}$

OPTIONS:

$n$
Corresponding to ${10}^{-n}$

RECOMMENDATION:

None

CIS_DER_NUMSTATE

Determines among how many states we calculate non-adiabatic couplings. These states must be
specified in the *$derivative_coupling* section.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not calculate non-adiabatic couplings.
$n$
Calculate $n(n-1)/2$ pairs of non-adiabatic couplings.

RECOMMENDATION:

None.

CIS_DIABATH_DECOMPOSE

Decide whether or not to decompose the diabatic coupling into Coulomb,
exchange, and one-electron terms.

TYPE:

LOGICAL

DEFAULT:

FALSE
Do not decompose the diabatic coupling.

OPTIONS:

TRUE

RECOMMENDATION:

These decompositions are most meaningful for electronic excitation transfer processes.
Currently, available only for CIS, not for TDDFT diabatic states.

CIS_DYNAMIC_MEM

Controls whether to use static or dynamic memory in CIS and TDDFT calculations.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Partly use static memory
TRUE
Fully use dynamic memory

RECOMMENDATION:

The default control requires static memory (MEM_STATIC) sufficient
to hold an array whose size grows by
$2\times OV\times {N}_{\text{roots}}$ at each CIS iteration, where ${N}_{\text{roots}}$
is the number of unconverged roots ($\le $ CIS_N_ROOTS).
For a large calculation, one has to specify a large value for MEM_STATIC,
which is not recommended (see Chapter 2). Therefore, it is
recommended to use dynamic memory for large calculations.

CIS_GUESS_DISK_TYPE

Determines the type of guesses to be read from disk

TYPE:

INTEGER

DEFAULT:

Nil

OPTIONS:

0
Read triplets only
1
Read triplets and singlets
2
Read singlets only

RECOMMENDATION:

Must be specified if CIS_GUESS_DISK is TRUE.

CIS_GUESS_DISK

Read the CIS guess from disk (previous calculation).

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Create a new guess.
TRUE
Read the guess from disk.

RECOMMENDATION:

Requires a guess from previous calculation.

CIS_MOMENTS

Controls calculation of excited-state (CIS or TDDFT) multipole moments.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not calculate excited-state moments.
TRUE
Calculate moments for each excited state.

RECOMMENDATION:

Set to TRUE if excited-state moments are desired. (This is a trivial
additional calculation.) The MULTIPOLE_ORDER controls how many
multipole moments are printed.

CIS_MULLIKEN

Controls Mulliken and Löwdin population analyses for excited-state particle and
hole density matrices.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not perform particle/hole population analysis.
TRUE
Perform both Mulliken and Löwdin analysis of the particle and hole
density matrices for each excited state.

RECOMMENDATION:

Set to TRUE if desired. This represents a trivial additional calculation.

CIS_N_ROOTS

Sets the number of excited state roots to find

TYPE:

INTEGER

DEFAULT:

0
Do not look for any excited states

OPTIONS:

$n$
$n>0$ Looks for $n$ excited states

RECOMMENDATION:

None

CIS_RELAXED_DENSITY

Use the relaxed CIS density for attachment/detachment density analysis as well
as for for the general excited-state analysis of Section 10.2.6.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not use the relaxed CIS density in analysis.
TRUE
Use the relaxed CIS density in analysis.

RECOMMENDATION:

None

CIS_S2_THRESH

Determines whether a state is a singlet or triplet in unrestricted calculations.

TYPE:

INTEGER

DEFAULT:

120

OPTIONS:

$n$
Sets the $\u27e8{\widehat{S}}^{2}\u27e9$ threshold to $n/100$

RECOMMENDATION:

For the default case, states with $\u27e8{\widehat{S}}^{2}\u27e9>1.2$ are treated as triplet states and
other states are treated as singlets.

CIS_SINGLETS

Solve for singlet excited states (ignored for spin unrestricted systems)

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
Solve for singlet states
FALSE
Do not solve for singlet states.

RECOMMENDATION:

None

CIS_STATE_DERIV

Sets CIS state for excited state optimizations and vibrational analysis.

TYPE:

INTEGER

DEFAULT:

0
Does not select any of the excited states.

OPTIONS:

$n$
Select the $n$th state.

RECOMMENDATION:

Check to see that the states do not change order during an optimization, due
to state crossings.

CIS_TRIPLETS

Solve for triplet excited states (ignored for spin unrestricted systems)

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
Solve for triplet states
FALSE
Do not solve for triplet states.

RECOMMENDATION:

None

CM5

Controls running of CM5 population analysis.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Calculate CM5 populations.
FALSE
Do not calculate CM5 populations.

RECOMMENDATION:

None

COMBINE_K

Controls separate or combined builds for short-range and long-range K

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE (or 0)
Build short-range and long-range K separately (twice as expensive as a global hybrid)
TRUE (or 1)
Build short-range and long-range K together ($\approx $ as expensive as a global hybrid)

RECOMMENDATION:

Most pre-defined range-separated hybrid functionals in Q-Chem use this
feature by default. However, if a user-specified RSH is desired, it is
necessary to manually turn this feature on.

COMPLEX_BASIS

Defines the complex basis.

TYPE:

STRING

DEFAULT:

No default complex basis set

OPTIONS:

Symbol
Use a standard basis set
ZBASIS_GENERAL, ZBASIS_GEN
User-defined. As for BASIS
ZBASIS_MIXED
User-defined mixed basis

RECOMMENDATION:

Consult Ref.
^{
1170
}
J. Chem. Phys.

(2015),
142,
pp. 054103.
Link
and the Basis Set Exchange.

COMPLEX_CCMAN

Requests complex-scaled or CAP-augmented CC/EOM calculations.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Engage complex CC/EOM code.

RECOMMENDATION:

Not available in CCMAN. Need to specify CAP strength or complex-scaling parameter
in *$complex_ccman* section.

COMPLEX_MIX

Mix a certain percentage of the real part of the HOMO to the
imaginary part of the LUMO.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0–100
The mix angle = $\pi \cdot $COMPLEX_MIX/100.

RECOMMENDATION:

It may help find the stable complex solution (similar idea as SCF_GUESS_MIX).

COMPLEX_THETA

Sets the value of $\theta $ in degrees for a calculation with complex basis functions.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
$\theta =n/10$ (degrees)

RECOMMENDATION:

Consult Ref.
^{
1170
}
J. Chem. Phys.

(2015),
142,
pp. 054103.
Link
. Usually calculations at several different values of $\theta $ (a “$\theta $-trajectory”) should be performed.

COMPLEX

Run an SCF calculation with complex MOs using GEN_SCFMAN.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

TRUE
Use complex orbitals.
FALSE
Use real orbitals.

RECOMMENDATION:

Set to TRUE if desired.

CORE_CHARACTER

Selects how the core orbitals are determined in the frozen-core
approximation.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Use energy-based definition.
1-4
Use Mulliken-based definition (see Table 6.1 for details).

RECOMMENDATION:

Use the default, unless performing calculations on molecules with heavy elements.

CORE_IONIZE

Indicates how orbitals are specified for reduced excitation spaces.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
all valence orbitals are listed in *$solute* section
2
only hole(s) are specified all other occupations same as ground state

RECOMMENDATION:

For MOM + TDDFT this specifies the input form of the *$solute* section. If set
to 1 all occupied orbitals must be specified, 2 only the empty orbitals to
ignore must be specified.

CORRELATION

Specifies the correlation level of theory handled by CCMAN/CCMAN2.

TYPE:

STRING

DEFAULT:

None
No Correlation

OPTIONS:

CCMP2
Regular MP2 handled by CCMAN/CCMAN2
MP3
CCMAN and CCMAN2
MP4SDQ
CCMAN
MP4
CCMAN
CCD
CCMAN and CCMAN2
CCD(2)
CCMAN
CCSD
CCMAN and CCMAN2
CC2
CCMAN2
CCSD(T)
CCMAN and CCMAN2
CCSD(2)
CCMAN
CCSD(fT)
CCMAN and CCMAN2
CCSD(dT)
CCMAN
CCVB-SD
CCMAN2
QCISD
CCMAN and CCMAN2
QCISD(T)
CCMAN and CCMAN2
OD
CCMAN
OD(T)
CCMAN
OD(2)
CCMAN
VOD
CCMAN
VOD(2)
CCMAN
QCCD
CCMAN
QCCD(T)
CCMAN
QCCD(2)
CCMAN
VQCCD
CCMAN
VQCCD(T)
CCMAN
VQCCD(2)
CCMAN

RECOMMENDATION:

Consult the literature for guidance.

CPSCF_NSEG

Controls the number of segments used to calculate the CPSCF equations.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not solve the CPSCF equations in segments.
$n$
User-defined. Use $n$ segments when solving the CPSCF equations.

RECOMMENDATION:

Use the default.

CUBEFILE_STATE

Determines which excited state is used to generate cube files

TYPE:

INTEGER

DEFAULT:

None

OPTIONS:

$n$
Generate cube files for the $n$th excited state

RECOMMENDATION:

None

CUDA_RI-MP2

Enables GPU implementation of RI-MP2

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
GPU-enabled MGEMM off
TRUE
GPU-enabled MGEMM on

RECOMMENDATION:

Necessary to set to 1 in order to run GPU-enabled RI-MP2

CUTOCC

Specifies occupied orbital cutoff.

TYPE:

INTEGER

DEFAULT:

50

OPTIONS:

0-200
CUTOFF = CUTOCC/100

RECOMMENDATION:

None

CUTVIR

Specifies virtual orbital cutoff.

TYPE:

INTEGER

DEFAULT:

0
No truncation

OPTIONS:

0-100
CUTOFF = CUTVIR/100

RECOMMENDATION:

None

CVS_EE_SINGLETS

Sets the number of singlet core-excited state roots to find. Valid only
for closed-shell references.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any excited states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ excited states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

CVS_EE_TRIPLETS

Sets the number of triplet core-excited state roots to find. Valid only
for closed-shell references.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any excited states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ excited states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

CVS_EOM_PRECONV_SINGLES

When not zero, singly excited vectors are converged prior to a full excited
states calculation (CVS states only). Sets the maximum number of iterations for pre-converging
procedure.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
do not pre-converge
1
pre-converge singles

RECOMMENDATION:

Sometimes helps with problematic convergence.

CVS_EOM_SHIFT

Specifies energy shift in CVS-EOM calculations.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
corresponds to $n\cdot {10}^{-3}$
hartree shift (*i.e.*, 11000 = 11 hartree); solve for
eigenstates around this value.

RECOMMENDATION:

Improves the stability of the calculations.

CVS_SF_STATES

Sets the number of core-level spin-flip target states roots to find.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any excited states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ SF states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DEA_AA_STATES

Sets the number of M${}_{s}$=1 DEA roots (two $\alpha $ electrons) to find.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DEA M${}_{s}$=1 transitions.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DEA $\alpha \alpha $ states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DEA_AB_STATES

Sets the number of M${}_{s}$=0 DEA roots (one $\alpha $ and one $\beta $ electron) to find.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DEA M${}_{s}$=0 transitions.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DEA $\alpha \beta $ states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DEA_BB_STATES

Sets the number of M${}_{s}$=-1 DEA roots (two $\beta $ electrons) to find.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DEA M${}_{s}$=-1 transitions.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DEA $\beta \beta $ states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DEA_SINGLETS

Sets the number of singlet DEA roots to find. Valid only
for closed-shell references.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any singlet DEA states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DEA singlet states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DEA_STATES

Sets the number of DEA roots to find. For
closed-shell reference, defaults into DEA_SINGLETS. For open-shell references,
specifies all low-lying states.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DEA states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DIP states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DEA_TRIPLETS

Sets the number of triplet DEA roots to find. Valid only
for closed-shell references.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DEA triplet states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DEA triplet states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DELTA_GRADIENT_SCALE

Scales the gradient of $\mathrm{\Delta}$ by $N$/100, which can be useful for cases with troublesome convergence by reducing step size.

TYPE:

INTEGER

DEFAULT:

100

OPTIONS:

$N$

RECOMMENDATION:

Use default. For problematic cases, $N=$50, 25, 10 or even $N=1$ could be useful.

DEUTERATE

Requests that all hydrogen atoms be replaces with deuterium.

TYPE:

LOGICAL

DEFAULT:

FALSE
Do not replace hydrogens.

OPTIONS:

TRUE
Replace hydrogens with deuterium.

RECOMMENDATION:

Replacing hydrogen atoms reduces the fastest vibrational frequencies by a
factor of 1.4, which allow for a larger fictitious mass and time step in ELMD
calculations. There is no reason to replace hydrogens in BOMD calculations.

DFPT_EXCHANGE

Specifies the secondary functional in a HFPC/DFPC calculation.

TYPE:

STRING

DEFAULT:

None

OPTIONS:

None

RECOMMENDATION:

See reference for recommended basis set, functional, and grid pairings.

DFPT_XC_GRID

Specifies the secondary grid in a HFPC/DFPC calculation.

TYPE:

STRING

DEFAULT:

None

OPTIONS:

None

RECOMMENDATION:

See reference for recommended basis set, functional, and grid pairings.

DFTVDW_ALPHA1

Parameter in XDM calculation with higher-order terms

TYPE:

INTEGER

DEFAULT:

83

OPTIONS:

10-1000

RECOMMENDATION:

None

DFTVDW_ALPHA2

Parameter in XDM calculation with higher-order terms.

TYPE:

INTEGER

DEFAULT:

155

OPTIONS:

10-1000

RECOMMENDATION:

None

DFTVDW_JOBNUMBER

Basic vdW job control

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not apply the XDM scheme.
1
Add vdW as energy/gradient correction to SCF.
2
Add vDW as a DFT functional and do full SCF (this option only works with XDM6).

RECOMMENDATION:

None

DFTVDW_KAI

Damping factor $k$ for ${C}_{6}$-only damping function

TYPE:

INTEGER

DEFAULT:

800

OPTIONS:

10–1000

RECOMMENDATION:

None

DFTVDW_METHOD

Choose the damping function used in XDM

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
Use Becke’s damping function including ${C}_{6}$ term only.
2
Use Becke’s damping function with higher-order (${C}_{8}$ and ${C}_{10}$) terms.

RECOMMENDATION:

None

DFTVDW_MOL1NATOMS

The number of atoms in the first monomer in dimer calculation

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0–${N}_{\mathrm{atoms}}$

RECOMMENDATION:

None

DFTVDW_PRINT

Printing control for VDW code

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

0
No printing.
1
Minimum printing (default)
2
Debug printing

RECOMMENDATION:

None

DFTVDW_USE_ELE_DRV

Specify whether to add the gradient correction to the XDM energy.
only valid with Becke’s ${C}_{6}$ damping function
using the interpolated BR89 model.

TYPE:

LOGICAL

DEFAULT:

1

OPTIONS:

1
Use density correction when applicable.
0
Do not use this correction (for debugging purposes).

RECOMMENDATION:

None

DFT_C

Controls whether the DFT-C empirical BSSE correction should be added.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
(or 0) Do not apply the DFT-C correction
TRUE
(or 1) Apply the DFT-C correction

RECOMMENDATION:

NONE

DFT_D3_3BODY

Controls whether the three-body interaction in Grimme’s DFT-D3 method should be applied
(see Eq. (14) in Ref. 383).

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE (or 0)
Do not apply the three-body interaction term
TRUE
Apply the three-body interaction term

RECOMMENDATION:

NONE

DFT_D3_POWER

The nonlinear parameter ${\beta}_{6}$ in Eq. (5.32). Used in
DFT-D3(op). Must be greater than or equal to 6 to avoid divergence.

TYPE:

INTEGER

DEFAULT:

600000

OPTIONS:

$n$
Corresponding to ${\beta}_{6}=n/100000$.

RECOMMENDATION:

NONE

DFT_D3_S6

The linear parameter ${s}_{6}$ in eq. (5.27). Used in all forms of DFT-D3.

TYPE:

INTEGER

DEFAULT:

100000

OPTIONS:

$n$
Corresponding to ${s}_{6}=n/100000$.

RECOMMENDATION:

NONE

DFT_D3_S8

The linear parameter ${s}_{8}$ in Eq. (5.27). Used in DFT-D3(0),
DFT-D3(BJ), DFT-D3M(0), DFT-D3M(BJ), and DFT-D3(op).

TYPE:

INTEGER

DEFAULT:

100000

OPTIONS:

$n$
Corresponding to ${s}_{8}=n/100000$.

RECOMMENDATION:

NONE

DFT_D4_A1

The nonlinear parameter ${\alpha}_{1}$. Used in DFT-D4.

TYPE:

INTEGER

DEFAULT:

Optimized number for the specified functional

OPTIONS:

$n$
Corresponding to ${\alpha}_{1}=n/100000000$.

RECOMMENDATION:

NONE

DFT_D4_A2

The nonlinear parameter ${\alpha}_{2}$. Used in DFT-D4.

TYPE:

INTEGER

DEFAULT:

Optimized number for the specified functional

OPTIONS:

$n$
Corresponding to ${\alpha}_{2}=n/100000000$.

RECOMMENDATION:

NONE

DFT_D4_GA

Charge scaling

TYPE:

INTEGER

DEFAULT:

300000000

OPTIONS:

$n$
Corresponding to $ga=n/100000000$.

RECOMMENDATION:

Use default

DFT_D4_GC

Charge scaling

TYPE:

INTEGER

DEFAULT:

200000000

OPTIONS:

$n$
Corresponding to $gc=n/100000000$.

RECOMMENDATION:

Use default

DFT_D4_S10

The linear parameter ${s}_{10}$. Used in DFT-D4.

TYPE:

INTEGER

DEFAULT:

Optimized number for the specified functional

OPTIONS:

$n$
Corresponding to ${s}_{10}=n/100000000$.

RECOMMENDATION:

NONE

DFT_D4_S6

The linear parameter ${s}_{6}$. Used in DFT-D4.

TYPE:

INTEGER

DEFAULT:

Optimized number for the specified functional

OPTIONS:

$n$
Corresponding to ${s}_{6}=n/100000000$.

RECOMMENDATION:

NONE

DFT_D4_S8

The linear parameter ${s}_{8}$. Used in DFT-D4.

TYPE:

INTEGER

DEFAULT:

Optimized number for the specified functional

OPTIONS:

$n$
Corresponding to ${s}_{8}=n/100000000$.

RECOMMENDATION:

NONE

DFT_D4_S9

The linear parameter ${s}_{9}$. Used in DFT-D4.

TYPE:

INTEGER

DEFAULT:

Optimized number for the specified functional

OPTIONS:

$n$
Corresponding to ${s}_{9}=n/100000000$.

RECOMMENDATION:

NONE

DFT_D4_WF

Weighting factor for Gaussian weighting.

TYPE:

INTEGER

DEFAULT:

600000000

OPTIONS:

$n$
Corresponding to $wf=n/100000000$.

RECOMMENDATION:

Use default

DFT_D_A

Controls the strength of dispersion corrections in the Chai–Head-Gordon DFT-D scheme, Eq. (5.26).

TYPE:

INTEGER

DEFAULT:

600

OPTIONS:

$n$
Corresponding to $a=n/100$.

RECOMMENDATION:

Use the default.

DFT_D

Controls the empirical dispersion correction to be added to a DFT calculation.

TYPE:

LOGICAL

DEFAULT:

None

OPTIONS:

FALSE
(or 0) Do not apply the DFT-D2, DFT-CHG, or DFT-D3 scheme
EMPIRICAL_GRIMME
DFT-D2 dispersion correction from Grimme
^{
390
}
J. Comput. Chem.

(2006),
27,
pp. 1787.
Link
EMPIRICAL_CHG
DFT-CHG dispersion correction from Chai and Head-Gordon
^{
180
}
Phys. Chem. Chem. Phys.

(2008),
10,
pp. 6615.
Link
EMPIRICAL_GRIMME3
DFT-D3(0) dispersion correction from Grimme (deprecated as
of Q-Chem 5.0)
D3_ZERO
DFT-D3(0) dispersion correction from Grimme *et al.*
^{
383
}
J. Chem. Phys.

(2010),
132,
pp. 154104.
Link
D3_BJ
DFT-D3(BJ) dispersion correction from Grimme *et al.*
^{
385
}
J. Comput. Chem.

(2011),
32,
pp. 1456.
Link
D3_CSO
DFT-D3(CSO) dispersion correction from Schröder *et al.*
^{
974
}
J. Chem. Theory Comput.

(2015),
11,
pp. 3163.
Link
D3_ZEROM
DFT-D3M(0) dispersion correction from Smith *et al.*
^{
1019
}
J. Phys. Chem. Lett.

(2016),
7,
pp. 2197.
Link
D3_BJM
DFT-D3M(BJ) dispersion correction from Smith *et al.*
^{
1019
}
J. Phys. Chem. Lett.

(2016),
7,
pp. 2197.
Link
D3_OP
DFT-D3(op) dispersion correction from Witte *et al.*
^{
1192
}
J. Chem. Theory Comput.

(2017),
13,
pp. 2043.
Link
D3
Automatically select the “best” available D3 dispersion correction
D4
DFT-D4 dispersion correction from Caldeweyher *et al.*
^{
144
}
J. Chem. Phys.

(2017),
147,
pp. 034112.
Link
^{,}
^{
145
}
J. Chem. Phys.

(2019),
150,
pp. 154122.
Link
^{,}
^{
146
}
Phys. Chem. Chem. Phys.

(2020),
22,
pp. 8499.
Link

RECOMMENDATION:

Use D4 if the specified functional is avialable. Currently, only a subset of functionals in DFT-D4 is supported.
It includes B3LYP, B97, B1LYP, PBE0, PW6B95, M06L, M06, WB97, WB97X, CAMB3LYP, PBE02, PBE0DH, MPW1K, MPWB1K, B1B95, B1PW91, B2GPPLYP, B2PLYP, B3P86, B3PW91, O3LYP, REVPBE,
REVPBE0, REVTPSS, REVTPSSH, SCAN, TPSS0, TPSSH, X3LYP, TPSS, BP86, BLYP, BPBE, MPW1PW91, MPW1LYP, PBE, RPBE, and PW91.

DH

Controls the application of DH-DFT scheme.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE (or 0)
Do not apply the DH-DFT scheme
TRUE (or 1)
Apply DH-DFT scheme

RECOMMENDATION:

NONE

DIIS_ERR_RMS

Changes the DIIS convergence metric from the maximum to the RMS error.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE, FALSE

RECOMMENDATION:

Use the default, the maximum error provides a more reliable criterion.

DIIS_PRINT

Controls the output from DIIS SCF optimization.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Minimal print out.
1
Chosen method and DIIS coefficients and solutions.
2
Level 1 plus changes in multipole moments.
3
Level 2 plus Multipole moments.
4
Level 3 plus extrapolated Fock matrices.

RECOMMENDATION:

Use the default

DIIS_SEPARATE_ERRVEC

Control optimization of DIIS error vector in unrestricted calculations.

TYPE:

LOGICAL

DEFAULT:

FALSE
Use a combined $\alpha $ and $\beta $ error vector.

OPTIONS:

FALSE
Use a combined $\alpha $ and $\beta $ error vector.
TRUE
Use separate error vectors for the $\alpha $ and $\beta $ spaces.

RECOMMENDATION:

When using DIIS in Q-Chem a convenient optimization for unrestricted
calculations is to sum the $\alpha $ and $\beta $ error vectors into a single
vector which is used for extrapolation. This is often extremely effective, but
in some pathological systems with symmetry breaking, can lead to false
solutions being detected, where the $\alpha $ and $\beta $ components of the
error vector cancel exactly giving a zero DIIS error. While an extremely
uncommon occurrence, if it is suspected, set
DIIS_SEPARATE_ERRVEC = TRUE to check.

DIIS_SUBSPACE_SIZE

Controls the size of the DIIS and/or RCA subspace during the SCF.

TYPE:

INTEGER

DEFAULT:

15

OPTIONS:

User-defined

RECOMMENDATION:

None

DIP_AA_STATES

Sets the number of M${}_{s}$=-1 DIP roots (remove two $\alpha $ electrons) to find. Valid only
for closed-shell references.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DIP M${}_{s}$=-1 states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DIP states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DIP_AB_STATES

Sets the number of M${}_{s}$=0 DIP roots (remove one $\alpha $ and one $\beta $ electron) to find.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DIP M${}_{s}$=0 states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DIP states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DIP_BB_STATES

Sets the number of M${}_{s}$=+1 DIP roots (remove two $\beta $ electrons) to find.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DIP M${}_{s}$=+1 states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DIP states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DIP_SINGLETS

Sets the number of singlet DIP roots to find. Valid only
for closed-shell references.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any singlet DIP states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DIP singlet states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DIP_STATES

Sets the number of DIP roots to find. For
closed-shell reference, defaults into DIP_SINGLETS. For open-shell references,
specifies all low-lying states.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DIP states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DIP states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DIP_TRIPLETS

Sets the number of triplet DIP roots to find. Valid only
for closed-shell references.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DIP triplet states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ DIP triplet states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DIRECT_SCF

Controls direct SCF.

TYPE:

LOGICAL

DEFAULT:

Determined by program.

OPTIONS:

TRUE
Forces direct SCF.
FALSE
Do not use direct SCF.

RECOMMENDATION:

Use the default; direct SCF switches off in-core integrals.

DISP_FREE_C

Specify the employed “dispersion-free" correlation functional.

TYPE:

STRING

DEFAULT:

NONE

OPTIONS:

Correlation functionals supported by Q-Chem.

RECOMMENDATION:

Put the appropriate correlation functional paired with the chosen exchange
functional (*e.g.* put PBE if DISP_FREE_X is revPBE); put
NONE if DISP_FREE_X is set to an exchange-correlation
functional.

DISP_FREE_X

Specify the employed “dispersion-free" exchange functional.

TYPE:

STRING

DEFAULT:

HF

OPTIONS:

Exchange functionals (*e.g.* revPBE) or exchange-correlation functionals (*e.g.* B3LYP)
supported by Q-Chem.

RECOMMENDATION:

HF is recommended for hybrid (primary) functionals (*e.g.*$\omega $B97X-V) and
revPBE for semi-local ones (*e.g.*B97M-V).
Other reasonable options (*e.g.* B3LYP for B3LYP-D3) can also be applied.

DOMODSANO

Specifies whether to do modified Sano or the original one

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Does original Sano procedure (similar to GVBMAN).
1
Does an improved Sano procedure that’s more localized.
2
Does another variation of Sano.

RECOMMENDATION:

1 is always better

DORAMAN

Controls calculation of Raman intensities. Requires JOBTYPE to be set
to FREQ

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not calculate Raman intensities.
TRUE
Do calculate Raman intensities.

RECOMMENDATION:

None

DSF_STATES

Sets the number of doubly spin-flipped target states roots to find.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not look for any DSF states.

OPTIONS:

$[i,j,k\mathrm{\dots}]$
Find $i$ doubly spin-flipped states in the first irrep, $j$ states
in the second irrep *etc.*

RECOMMENDATION:

None

DUAL_BASIS_ENERGY

Activates dual-basis SCF (HF or DFT) energy correction.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

Analytic first derivative available for HF and DFT (see JOBTYPE)
Can be used in conjunction with MP2 or RI-MP2
See BASIS, BASIS2, BASISPROJTYPE

RECOMMENDATION:

Use dual-basis to capture large-basis effects at smaller basis cost.
Particularly useful with RI-MP2, in which HF often dominates. Use only proper
subsets for small-basis calculation.

D_CPSCF_PERTNUM

Specifies whether to do the perturbations one at a time, or all together.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Perturbed densities to be calculated all together.
1
Perturbed densities to be calculated one at a time.

RECOMMENDATION:

None

D_SCF_CONV_1

Sets the convergence criterion for the level-1 iterations. This preconditions
the density for the level-2 calculation, and does not include any
two-electron integrals.

TYPE:

INTEGER

DEFAULT:

4
corresponding to a threshold of ${10}^{-4}$.

OPTIONS:

$$
Sets convergence threshold to ${10}^{-n}$.

RECOMMENDATION:

The criterion for level-1 convergence must be less than or equal to the
level-2 criterion, otherwise the D-CPSCF will not converge.

D_SCF_CONV_2

Sets the convergence criterion for the level-2 iterations.

TYPE:

INTEGER

DEFAULT:

4
Corresponding to a threshold of ${10}^{-4}$.

OPTIONS:

$$
Sets convergence threshold to ${10}^{-n}$.

RECOMMENDATION:

None

D_SCF_DIIS

Specifies the number of matrices to use in the DIIS extrapolation in the
D-CPSCF.

TYPE:

INTEGER

DEFAULT:

11

OPTIONS:

$n$
$n$ = 0 specifies no DIIS extrapolation is to be used.

RECOMMENDATION:

Use the default.

D_SCF_MAX_1

Sets the maximum number of level-1 iterations.

TYPE:

INTEGER

DEFAULT:

100

OPTIONS:

$n$
User defined.

RECOMMENDATION:

Use the default.

D_SCF_MAX_2

Sets the maximum number of level-2 iterations.

TYPE:

INTEGER

DEFAULT:

30

OPTIONS:

$n$ User defined.

RECOMMENDATION:

Use the default.

EA_STATES

Controls the number of electron-attached states to calculate.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not perform an EA-ADC calculation

OPTIONS:

$n>0$
Number of states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep, ${n}_{2}$ states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of electron-attached states in case of
restricted calculations.

ECP

Defines the effective core potential and associated basis set to be used

TYPE:

STRING

DEFAULT:

No ECP

OPTIONS:

General, Gen
User defined. (*$ecp* keyword required)
Symbol
Use standard ECPs discussed above.

RECOMMENDATION:

ECPs are recommended for first row transition metals and heavier
elements. Consult the reviews for more details.

EDA2

Switch on EDA2 and specify the option set number.

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

0
Do not run through EDA2.
1
Frozen energy decomposition + nDQ-FERF polarization
(the standard EDA2 option)
2
Frozen energy decomposition + (AO-block-based) ALMO polarization
(old scheme with the addition of frozen decomposition)
3
Frozen energy decomposition + oDQ-FERF polarization
(NOT commonly used)
4
Frozen wave function relaxation + Frozen energy decomposition + nDQ-FERF polarization
(NOT commonly used)
5
Frozen energy decomposition + polMO polarization
(NOT commonly used).
10
No preset. Completely controlled by user’s *$rem* input
(for developers only)

RECOMMENDATION:

Turn on EDA2 for Q-Chem’s ALMO-EDA jobs unless CTA with the old
scheme is desired. Option 1 is recommended in general, especially when
substantially large basis sets are employed. The original ALMO scheme (option
2) can be used when the employed basis set is of small or medium size (arguably
no larger than augmented triple-$\zeta $). The other options are rarely used for
routine applications.

EDA_BSSE

Calculates the BSSE correction when performing the energy decomposition
analysis.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

Set to TRUE unless a very large basis set is used.

EDA_CLS_DISP

Compute the DISP contribution without performing the orthogonal decomposition,
which will then be subtracted from the classical PAULI term.

TYPE:

BOOLEAN

DEFAULT:

FALSE

OPTIONS:

FALSE
Use the DISP term computed with orthogonal decomposition (if available).
TRUE
Use the DISP term computed using undistorted monomer densities.

RECOMMENDATION:

Set it to TRUE when orthogonal decomposition is not performed.

EDA_CLS_ELEC

Perform the classical decomposition of the frozen term.

TYPE:

BOOLEAN

DEFAULT:

FALSE (automatically set to TRUE by EDA2 options 1–5)

OPTIONS:

FALSE
Do not compute the classical ELEC and PAULI terms.
TRUE
Perform the classical decomposition.

RECOMMENDATION:

TRUE

EDA_CONTRACTION_ANAL

Perform analysis separating orbital contraction from the rest of POL.

TYPE:

BOOLEAN

DEFAULT:

0

OPTIONS:

FALSE
Do not perform contraction analysis.
TRUE
Perform contraction analysis.

RECOMMENDATION:

No recommendation

EDA_COVP

Perform COVP analysis when evaluating the RS or ARS
charge-transfer correction. COVP analysis is currently implemented only for
systems of two fragments.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

Set to TRUE to perform COVP analysis in an EDA or SCF MI(RS) job.

EDA_PRINT_COVP

Replace the final MOs with the CVOP orbitals in the end of the run.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE/FALSE

RECOMMENDATION:

Set to TRUE to print COVP orbitals instead of conventional MOs.

EE_SINGLETS

Controls the number of singlet excited states to calculate.

TYPE:

INTEGER/ARRAY

DEFAULT:

0
Do not perform an ADC calculation of singlet excited states

OPTIONS:

$n>0$
Number of singlet states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep, ${n}_{2}$
states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of excited states in case of restricted
calculations of singlet states. In unrestricted calculations it can also be
used, if EE_STATES not set. Then, it has the same effect as setting
EE_STATES.

EE_STATES

Controls the number of excited states to calculate.

TYPE:

INTEGER/ARRAY

DEFAULT:

0
Do not perform an ADC calculation

OPTIONS:

$n>0$
Number of states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep, ${n}_{2}$ states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of excited states in case of
unrestricted or open-shell calculations. In restricted calculations it can also
be used, if neither EE_SINGLETS nor EE_TRIPLETS is given.
Then, it has the same effect as setting EE_SINGLETS.

EE_TRIPLETS

Controls the number of triplet excited states to calculate.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not perform an ADC calculation of triplet excited states

OPTIONS:

$n>0$
Number of triplet states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep, ${n}_{2}$
states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of excited states in case of restricted
calculations of triplet
states.

EFP_COORD_XYZ

Use coordinates of three atoms instead of Euler angles to specify
position and orientation of the fragments

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE FALSE

RECOMMENDATION:

None

EFP_DIRECT_POLARIZATION_DRIVER

Use direct solver for EFP polarization

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE FALSE

RECOMMENDATION:

Direct polarization solver provides stable convergence of induced dipoles which may otherwise become problematic in case of closely lying or highly polar or charged fragments. The computational cost of direct polarization versus iterative polarization becomes higher for systems containing more than 10000 polarizable points.

EFP_DISP_DAMP

Controls fragment-fragment dispersion screening in EFP

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

0
switch off dispersion screening
1
use Tang-Toennies screening, with fixed parameter $b=1.5$
2
use overlap-based damping

RECOMMENDATION:

None

EFP_DISP

Controls fragment-fragment dispersion in EFP

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
switch on dispersion
FALSE
switch off dispersion

RECOMMENDATION:

None

EFP_ELEC_DAMP

Controls fragment-fragment electrostatic screening in EFP

TYPE:

INTEGER

DEFAULT:

2

OPTIONS:

0
switch off electrostatic screening
1
use overlap-based damping correction
2
use exponential damping correction if screening parameters are provided in the EFP potential

RECOMMENDATION:

Overlap-based damping is recommended

EFP_ELEC

Controls fragment-fragment electrostatics in EFP

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
switch on electrostatics
FALSE
switch off electrostatics

RECOMMENDATION:

None

EFP_ENABLE_LINKS

Enable fragment links in EFP region

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE FALSE

RECOMMENDATION:

None

EFP_EXREP

Controls fragment-fragment exchange repulsion in EFP

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
switch on exchange repulsion
FALSE
switch off exchange repulsion

RECOMMENDATION:

None

EFP_FRAGMENTS_ONLY

Specifies whether there is a QM part

TYPE:

LOGICAL

DEFAULT:

FALSE
QM part is present

OPTIONS:

TRUE
Only MM part is present: all fragments are treated by EFP
FALSE
QM part is present: do QM/MM EFP calculation

RECOMMENDATION:

None

EFP_INPUT

Specifies the format of EFP input

TYPE:

LOGICAL

DEFAULT:

FALSE
Dummy atom (*e.g.*, He) in *$molecule* section should be present

OPTIONS:

TRUE
A format without dummy atom in *$molecule* section
FALSE
A format with dummy atom in *$molecule* section

RECOMMENDATION:

None

EFP_POL_DAMP

Controls fragment-fragment polarization screening in EFP

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

0
switch off polarization screening
1
use Tang-Toennies screening

RECOMMENDATION:

None

EFP_POL

Controls fragment-fragment polarization in EFP

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
switch on polarization
FALSE
switch off polarization

RECOMMENDATION:

None

EFP_QM_DISP

Controls QM-EFP dispersion

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
switch on QM-EFP dispersion
FALSE
switch off QM-EFP dispersion

RECOMMENDATION:

None

EFP_QM_ELEC_DAMP

Controls QM-EFP electrostatics screening in EFP

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
switch off electrostatic screening
1
use overlap based damping correction

RECOMMENDATION:

None

EFP_QM_ELEC

Controls QM-EFP electrostatics

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
switch on QM-EFP electrostatics
FALSE
switch off QM-EFP electrostatics

RECOMMENDATION:

None

EFP_QM_EXREP

Controls QM-EFP exchange-repulsion

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
switch on QM-EFP exchange-repulsion
FALSE
switch off QM-EFP exchange-repulsion

RECOMMENDATION:

None

EFP_QM_POL

Controls QM-EFP polarization

TYPE:

LOGICAL

DEFAULT:

TRUE

OPTIONS:

TRUE
switch on QM-EFP polarization
FALSE
switch off QM-EFP polarization

RECOMMENDATION:

None

EFP

Specifies that EFP calculation is requested

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE FALSE

RECOMMENDATION:

The keyword should be present if excited state calculation is requested

EMBEDMAN

Turns density embedding on.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not use density embedding.
1
Turn on density embedding.

RECOMMENDATION:

Use EMBEDMAN for QM/QM density embedded calculations.

EMBED_MU

Specifies exponent value of projection operator scaling factor, $\mu $
[Eqs. (11.104) and (11.106)].

TYPE:

INTEGER

DEFAULT:

7

OPTIONS:

n
$\mu ={10}^{n}$.

RECOMMENDATION:

Values of 2 - 7 are recommended. A higher value of $\mu $ leads to better
orthogonality of the fragment MOs but $\mu >{10}^{7}$ introduces numerical
noise. $$ results in non-additive terms becoming too large. Energy
corrections are fairly insensitive to changes in $\mu $ within the range of
${10}^{2}-{10}^{7}$.

EMBED_THEORY

Specifies post-DFT method performed on fragment one.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
No post HF method, only DFT on fragment one.
1
Perform CCSD(T) calculation on fragment one.
2
Perform MP2 calculation on fragment one.

RECOMMENDATION:

This should be 1 or 2 for the high-level QM calculation of fragment
1-in-2, and 0 for fragment 2-in-1 low-level QM calculation.

EMBED_THRESH

Specifies threshold cutoff for AO contribution used to determine which MOs
belong to which fragments

TYPE:

INTEGER

DEFAULT:

500

OPTIONS:

n
Threshold $=n/1000$

RECOMMENDATION:

Acceptable values range from 0 to 1000. Should only need to be tuned for
non-highly localized MOs

EOM_ARESP_SINGLE_PREC

Precision selection for amplitude response EOM equations. Available in CCMAN2 only.

TYPE:

INTEGER

DEFAULT:

0
double-precision calculation

OPTIONS:

1
single-precision calculation

RECOMMENDATION:

NONE

EOM_CORR

Specifies the correlation level.

TYPE:

STRING

DEFAULT:

None
No correction will be computed

OPTIONS:

SD(DT)
EOM-CCSD(dT), available for EE, SF, and IP
SD(FT)
EOM-CCSD(fT), available for EE, SF, IP, and EA
SD(ST)
EOM-CCSD(sT), available for IP

RECOMMENDATION:

None

EOM_DAVIDSON_CONVERGENCE

Convergence criterion for the RMS residuals of excited state vectors.

TYPE:

INTEGER

DEFAULT:

5
Corresponding to ${10}^{-5}$

OPTIONS:

$n$
Corresponding to ${10}^{-n}$ convergence criterion

RECOMMENDATION:

Use the default. Normally this value be the same as EOM_DAVIDSON_THRESHOLD.

EOM_DAVIDSON_MAXVECTORS

Specifies maximum number of vectors in the subspace for the Davidson
diagonalization.

TYPE:

INTEGER

DEFAULT:

60

OPTIONS:

$n$
Up to $n$ vectors per root before the subspace is reset

RECOMMENDATION:

Larger values increase disk storage but accelerate and stabilize convergence.

EOM_DAVIDSON_MAX_ITER

Maximum number of iteration allowed for Davidson diagonalization procedure.

TYPE:

INTEGER

DEFAULT:

30

OPTIONS:

$n$
User-defined number of iterations

RECOMMENDATION:

Default is usually sufficient

EOM_DAVIDSON_THRESHOLD

Specifies threshold for including a new expansion vector in the iterative
Davidson diagonalization. Their norm must be above this threshold.

TYPE:

INTEGER

DEFAULT:

00103
Corresponding to 0.00001

OPTIONS:

$abcde$
Integer code is mapped to $abc\times {10}^{-(de+2)}$, *i.e.*, 02505->2.5$\times {10}^{-6}$

RECOMMENDATION:

Use the default unless converge problems are encountered. Should normally be set
to the same values as EOM_DAVIDSON_CONVERGENCE, if convergence problems arise
try setting to a value slightly larger than EOM_DAVIDSON_CONVERGENCE.

EOM_EA_ALPHA

Controls the number of $\alpha $-electron-attached states to calculate.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not compute $\alpha $-electron-attached states

OPTIONS:

$n>0$
Number of $\alpha $-electron-attached states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ $\alpha $-electron-attached states for the first irrep,
${n}_{2}$ $\alpha $-electron-attached states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of $\alpha $-electron-attached states in case of
unrestricted or open-shell calculations.

EOM_EA_BETA

Controls the number of $\beta $-electron-attached states to calculate.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not compute $\beta $-electron-attached states

OPTIONS:

$n>0$
Number of $\beta $-electron-attached states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ $\beta $-electron-attached states for the first irrep,
${n}_{2}$ $\beta $-electron-attached states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of $\beta $-electron-attached states in case of
unrestricted or open-shell calculations.

EOM_FAKE_IPEA

If TRUE, calculates fake EOM-IP or EOM-EA energies and properties
using the diffuse orbital trick. Default for EOM-EA and Dyson orbital
calculations in CCMAN.

TYPE:

LOGICAL

DEFAULT:

FALSE (use proper EOM-IP code)

OPTIONS:

FALSE, TRUE

RECOMMENDATION:

None. This feature only works for CCMAN.

EOM_IPEA_FILTER

If TRUE, filters the EOM-IP/EA amplitudes obtained using the diffuse
orbital implementation (see EOM_FAKE_IPEA). Helps with convergence.

TYPE:

LOGICAL

DEFAULT:

FALSE (EOM-IP or EOM-EA amplitudes will not be filtered)

OPTIONS:

FALSE, TRUE

RECOMMENDATION:

None

EOM_IP_ALPHA

Controls the number of $\alpha $-ionized states to calculate.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not compute $\alpha $-ionized states

OPTIONS:

$n>0$
Number of $\alpha $-ionized states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ $\alpha $-ionized states for the first irrep,
${n}_{2}$ $\alpha $-ionized states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of $\alpha $-ionized states in case of
unrestricted or open-shell calculations.

EOM_IP_BETA

Controls the number of $\beta $-ionized states to calculate.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not compute $\beta $-ionized states

OPTIONS:

$n>0$
Number of $\beta $-ionized states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ $\beta $-ionized states for the first irrep,
${n}_{2}$ $\beta $-ionized states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of $\beta $-ionized states in case of
unrestricted or open-shell calculations.

EOM_NGUESS_DOUBLES

Specifies number of excited state guess vectors which are double excitations.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Include $n$ guess vectors that are double excitations

RECOMMENDATION:

This should be set to the expected number of doubly excited states,
otherwise they may not be found.

EOM_NGUESS_SINGLES

Specifies number of excited state guess vectors that are single excitations.

TYPE:

INTEGER

DEFAULT:

Equal to the number of excited states requested

OPTIONS:

$n$
Include $n$ guess vectors that are single excitations

RECOMMENDATION:

Should be greater or equal than the number of excited states requested, unless
.

EOM_POL

Specifies the approach for calculating the polarizability of the EOM-CCSD wave function.

TYPE:

INTEGER

DEFAULT:

0
(EOM-CCSD polarizability will not be calculated)

OPTIONS:

1
(analytic-derivative or response-theory mixed symmetric-asymmetric approach)
2
(analytic-derivative or response-theory asymmetric approach)
3
(expectation-value approach with right response intermediates)
4
(expectation-value approach with left response intermediates)

RECOMMENDATION:

EOM-CCSD polarizabilities are expensive since they require solving
three/nine (for static) or six/eighteen (for dynamical)
additional response equations. Do no request this property unless you need it.

EOM_PRECONV_DOUBLES

When not zero, doubly excited vectors are converged prior to a full excited
states calculation. Sets the maximum number of iterations for pre-converging procedure

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Do not pre-converge
N
Perform N Davidson iterations pre-converging doubles.

RECOMMENDATION:

Occasionally necessary to ensure a doubly excited state is found. Also used in DSF, DIP, and DEA calculations
instead of EOM_PRECONV_SINGLES

EOM_PRECONV_SD

When not zero, EOM vectors are pre-converged prior to a full excited states
calculation. Sets the maximum number of iterations for pre-converging
procedure.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
do not pre-converge
N
perform N Davidson iterations pre-converging singles and doubles.

RECOMMENDATION:

Occasionally necessary to ensure that all low-lying states are
found. Also, very useful in EOM(2,3) calculations.

None

EOM_PRECONV_SINGLES

When not zero, singly excited vectors are converged prior to a full excited
states calculation. Sets the maximum number of iterations for pre-converging
procedure.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
do not pre-converge
1
pre-converge singles

RECOMMENDATION:

Sometimes helps with problematic convergence.

EOM_SHIFT

Specifies energy shift in EOM calculations.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
corresponds to $n\cdot {10}^{-3}$
hartree shift (*i.e.*, 11000 = 11 hartree); solve for
eigenstates around this value.

RECOMMENDATION:

Not available in CCMAN.

EOM_SINGLE_PREC

Precision selection for EOM-CC/MP2 calculations. Available in CCMAN2 only.

TYPE:

INTEGER

DEFAULT:

0
double-precision calculation

OPTIONS:

1
single-precision calculation
2
single-precision calculation is followed by double-precision clean-up iterations

RECOMMENDATION:

Do not set too tight convergence criteria when use single precision

EOM_USER_GUESS

Specifies if user-defined guess will be used in EOM calculations.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Solve for a state that has maximum overlap with a trans-n
specified in *$eom_user_guess*.

RECOMMENDATION:

The orbitals are ordered by energy, as printed in the beginning of the
CCMAN2 output. Not available in CCMAN.

EPAO_ITERATE

Controls iterations for EPAO calculations (see PAO_METHOD).

TYPE:

INTEGER

DEFAULT:

0
Use non-iterated EPAOs based on atomic blocks of SPS.

OPTIONS:

$n$
Optimize the EPAOs for up to $n$ iterations.

RECOMMENDATION:

Use the default. For molecules that are not too large, one can test the
sensitivity of the results to the type of minimal functions by the use of
optimized EPAOs in which case a value of $n=500$ is reasonable.

EPAO_WEIGHTS

Controls algorithm and weights for EPAO calculations (see PAO_METHOD).

TYPE:

INTEGER

DEFAULT:

115
Standard weights, use 1${}^{\mathrm{st}}$ and 2${}^{\mathrm{nd}}$ order optimization

OPTIONS:

15
Standard weights, with 1${}^{\mathrm{st}}$ order optimization only.

RECOMMENDATION:

Use the default, unless convergence failure is encountered.

ERCALC

Specifies the Edmiston-Ruedenberg localized orbitals are to be calculated

TYPE:

INTEGER

DEFAULT:

06000

OPTIONS:

$aabcd$
$aa$
specifies the convergence threshold.
If $aa>3$, the threshold is set to ${10}^{-aa}$. The default is 6.
If $aa=1$, the calculation is aborted after the guess, allowing Pipek-Mezey
orbitals to be extracted.
$b$
specifies the guess:
0 Boys localized orbitals. This is the default
1 Pipek-Mezey localized orbitals.
$c$
specifies restart options (if restarting from an ER calculation):
0 No restart. This is the default
1 Read in MOs from last ER calculation.
2 Read in MOs and RI integrals from last ER calculation.
$d$
specifies how to treat core orbitals
0 Do not perform ER localization. This is the default.
1 Localize core and valence together.
2 Do separate localizations on core and valence.
3 Localize only the valence electrons.
4 Use the *$localize* section.

RECOMMENDATION:

ERCALC 1 will usually suffice, which uses threshold ${10}^{-6}$.

ER_CIS_NUMSTATE

Define how many states to mix with ER localized diabatization. These states must be specified
in the *$localized_diabatization* section.

TYPE:

INTEGER

DEFAULT:

0
Do not perform ER localized diabatization.

OPTIONS:

2 to N where N is the number of CIS states requested (CIS_N_ROOTS)

RECOMMENDATION:

It is usually not wise to mix adiabatic states that are separated by more than a few eV
or a typical reorganization energy in solvent.

ESP_CHARGES

Controls the calculations of Merz-Kollman ESP-derived charges.

TYPE:

INTEGER

DEFAULT:

NONE

OPTIONS:

1
Use Lebedev grid points around each atom.
2
Use spherical harmonics grid points around each atom.

RECOMMENDATION:

NONE

ESP_EFIELD

Triggers the calculation of the electrostatic potential (ESP) and/or the electric field
at the positions of the MM charges.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Computes ESP only.
1
Computes ESP and electric field.
2
Computes electric field only.

RECOMMENDATION:

None.

ESP_GRID

Controls evaluation of the electrostatic potential on a grid of points. If
enabled, the output is in an ASCII file, plot.esp, in the format $x,y,z,$ esp
for each point.

TYPE:

INTEGER

DEFAULT:

none no electrostatic potential evaluation

OPTIONS:

$-3$
same as the option $-1$ but in connection with STATE_ANALYSIS = TRUE.
This computes the ESP for all excited-state densities, transition densities,
and electron/hole densities.
$-2$
same as the option $-1$, plus evaluate the ESP of the *$external_charges*
$-1$
read grid input via the *$plots* section of the input deck
$0$
Generate the ESP values at all nuclear positions
+$n$
read $n$ grid points in bohr from the ASCII file ESPGrid

RECOMMENDATION:

None

ESP_SURFACE_DENSITY

Controls the spacing between grid points on vdW surfaces.

TYPE:

INTEGER

DEFAULT:

500

OPTIONS:

$n$
Spacing of $0.001\times n$ (in Å)

RECOMMENDATION:

The default corresponds to 0.5 Å spacing.

ESP_TRANS

Controls the calculation of the electrostatic potential of the transition density

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
compute the electrostatic potential of the excited state transition density
FALSE
compute the electrostatic potential of the excited state electronic density

RECOMMENDATION:

NONE

EXCHANGE

Specifies the exchange functional (or most exchange-correlation functionals for backwards compatibility).

TYPE:

STRING

DEFAULT:

No default

OPTIONS:

*NAME*
Use EXCHANGE = *NAME*, where *NAME* is either:
1) One of the exchange functionals listed in Section 5.3.2
2) One of the XC functionals listed in Section 5.3.4
that is not marked with an
asterisk.
3) GEN, for a user-defined functional (see Section 5.3.6).

RECOMMENDATION:

In general, consult the literature to guide your selection. Our recommendations are indicated in bold in Sections 5.3.4 and 5.3.2.

FAST_XAS

Controls whether fast TDDFT for core excitations is used.

TYPE:

LOGICAL

DEFAULT:

FALSE
Normal TDDFT calculation.

OPTIONS:

TRUE
Use fast TDDFT.

RECOMMENDATION:

None

FAST_XC

Controls direct variable thresholds to accelerate exchange-correlation (XC) in
DFT.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Turn FAST_XC on.
FALSE
Do not use FAST_XC.

RECOMMENDATION:

Caution: FAST_XC improves the speed of a DFT calculation, but
may occasionally cause the SCF calculation to diverge.

FDE

Turns density embedding on.

TYPE:

BOOLEAN

DEFAULT:

False

OPTIONS:

True
Perform an FDET calculation.
False
Don’t perform FDET calculation.

RECOMMENDATION:

Set the *$rem* variable FDE to TRUE to start a FDET calculation.

FDIFF_DER

Controls what types of information are used to compute higher
derivatives. The default uses a combination of energy, gradient and Hessian
information, which makes the force field calculation faster.

TYPE:

INTEGER

DEFAULT:

3
for jobs where analytical 2nd derivatives are available.
0
for jobs with ECP.

OPTIONS:

0
Use energy information only.
1
Use gradient information only.
2
Use Hessian information only.
3
Use energy, gradient, and Hessian information.

RECOMMENDATION:

When the molecule is larger than benzene with small basis set,
FDIFF_DER = 2 may be faster. Note that FDIFF_DER will be set
lower if analytic derivatives of the requested order are not available. Please
refers to IDERIV.

FDIFF_STEPSIZE_QFF

Displacement used for calculating third and fourth derivatives by finite difference.

TYPE:

INTEGER

DEFAULT:

5291
Corresponding to 0.1 bohr. For calculating third and fourth derivatives.

OPTIONS:

$n$
Use a step size of $n\times {10}^{-5}$.

RECOMMENDATION:

Use the default, unless the potential surface is very flat, in which case a larger value
should be used.

FDIFF_STEPSIZE

Displacement used for calculating derivatives by finite difference.

TYPE:

INTEGER

DEFAULT:

100
Corresponding to 0.001 Å. For calculating second derivatives.

OPTIONS:

$n$
Use a step size of $n\times {10}^{-5}$.

RECOMMENDATION:

Use the default except in cases where the potential surface is very flat, in
which case a larger value should be used. See FDIFF_STEPSIZE_QFF for third
and fourth derivatives.

FD_MAT_VEC_PROD

Compute Hessian-vector product using the finite difference technique.

TYPE:

BOOLEAN

DEFAULT:

FALSE (TRUE when the employed functional contains NLC)

OPTIONS:

FALSE
Compute Hessian-vector product analytically.
TRUE
Use finite difference to compute Hessian-vector product.

RECOMMENDATION:

Set it to TRUE when analytical Hessian is not available.
Note:
For simple R and U calculations, it can always be set to FALSE, which
indicates that
only the NLC part will be computed with finite difference.

FEFP_EFP

Specifies that fEFP_EFP calculation is requested to compute the total
interaction energies between a ligand (the last fragment in the
$efp_fragments section) and the protein (represented by fEFP)

TYPE:

STRING

DEFAULT:

OFF

OPTIONS:

OFF
disables fEFP
LA
enables fEFP with the Link Atom (HLA or CLA) scheme (only
electrostatics and polarization)
MFCC
enables fEFP with MFCC (only
electrostatics)

RECOMMENDATION:

The keyword should be invoked if EFP/fEFP is requested (interaction
energy calculations). This keyword has to be employed with
EFP_FRAGMENT_ONLY = TRUE. To switch on/off
electrostatics or polarzation interactions, the usual EFP controls are
employed.

FEFP_QM

Specifies that fEFP_QM calculation is requested to perform a
QM/fEFPcompute computation. The fEFP part is a fractionated macromolecule.

TYPE:

STRING

DEFAULT:

OFF

OPTIONS:

OFF
disables fEFP_QM and performs a QM/EFP calculation
LA
enables fEFP_QM with the Link Atom scheme

RECOMMENDATION:

The keyword should be invoked if QM/fEFP is requested. This keyword has
to be employed with efp_fragment_only false. Only electrostatics is
available.

FOA_FUNDGAP

Compute the frozen-orbital approximation of the fundamental gap.

TYPE:

Boolean

DEFAULT:

FALSE

OPTIONS:

FALSE
Do not compute FOA derivative discontinuity and fundamental gap.
TRUE
Compute and print FOA fundamental gap information. Implies KS_GAP_PRINT.

RECOMMENDATION:

Use in conjunction with KS_GAP_UNIT if true.

FOCK_EXTRAP_ORDER

Specifies the polynomial order $N$ for Fock matrix extrapolation.

TYPE:

INTEGER

DEFAULT:

0
Do not perform Fock matrix extrapolation.

OPTIONS:

$N$
Extrapolate using an $N$th-order polynomial ($N>0$).

RECOMMENDATION:

None

FOCK_EXTRAP_POINTS

Specifies the number $M$ of old Fock matrices that are retained for use in
extrapolation.

TYPE:

INTEGER

DEFAULT:

0
Do not perform Fock matrix extrapolation.

OPTIONS:

$M$
Save $M$ Fock matrices for use in extrapolation $(M>N)$

RECOMMENDATION:

Higher-order extrapolations with more saved Fock matrices are faster and
conserve energy better than low-order extrapolations, up to a point. In many
cases, the scheme ($N$ = 6, $M$ = 12), in conjunction with
SCF_CONVERGENCE = 6, is found to provide about a 50% savings in
computational cost while still conserving energy.

FOLLOW_ENERGY

Adjusts the energy window for near states

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Use dynamic thresholds, based on energy difference between steps.
$n$
Search over selected state ${E}_{\mathrm{est}}\pm n\times {10}^{-6}{E}_{h}$.

RECOMMENDATION:

Use a wider energy window to follow a state diabatically, smaller window to
remain on the adiabatic state most of the time.

FOLLOW_OVERLAP

Adjusts the threshold for states of similar character.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Use dynamic thresholds, based on energy difference between steps.
$n$
Percentage overlap for previous step and current step.

RECOMMENDATION:

Use a higher value to require states have higher degree of similarity to be
considered the same (more often selected based on energy).

FON_E_THRESH

DIIS error below which occupations will be kept constant.

TYPE:

INTEGER

DEFAULT:

4

OPTIONS:

$n$
freeze occupations below DIIS error of ${10}^{-n}$

RECOMMENDATION:

This should be one or two numbers bigger than the desired SCF convergence
threshold.

FON_NORB

Number of orbitals above and below the Fermi level that are allowed to have
fractional occupancies.

TYPE:

INTEGER

DEFAULT:

4

OPTIONS:

$n$
number of active orbitals

RECOMMENDATION:

The number of valence orbitals is a reasonable choice.

FON_T_END

Final electronic temperature for FON calculation.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

Any desired final temperature.

RECOMMENDATION:

Pick the temperature to either reproduce experimental conditions (*e.g.* room
temperature) or as low as possible to approach zero-temperature.

FON_T_METHOD

Selects cooling algorithm.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

1
temperature is scaled by a factor in each cycle
2
temperature is decreased by a constant number in each cycle

RECOMMENDATION:

We have made slightly better experience with a constant cooling rate. However,
choose constant temperature when in doubt.

FON_T_SCALE

Determines the step size for the cooling.

TYPE:

INTEGER

DEFAULT:

90

OPTIONS:

$n$
temperature is scaled by $0.01\cdot n$ in each cycle (cooling method 1)
$n$
temperature is decreased by n K in each cycle (cooling method 2)

RECOMMENDATION:

The cooling rate should be neither too slow nor too fast. Too slow may lead to
final energies that are at undesirably high temperatures. Too fast may lead to
convergence issues. Reasonable choices for methods 1 and 2 are 98 and 50,
respectively. When in doubt, use constant temperature.

FON_T_START

Initial electronic temperature (in K) for FON calculation.

TYPE:

INTEGER

DEFAULT:

1000

OPTIONS:

Any desired initial temperature.

RECOMMENDATION:

Pick the temperature to either reproduce experimental conditions (*e.g.* room
temperature) or as low as possible to approach zero-temperature.

FORCE_FIELD

Specifies the force field for MM energies in QM/MM calculations.

TYPE:

STRING

DEFAULT:

NONE

OPTIONS:

AMBER99
AMBER99 force field
CHARMM27
CHARMM27 force field
OPLSAA
OPLSAA force field

RECOMMENDATION:

None.

FRACTIONAL_ELECTRON

Add or subtract a fraction of an electron.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Use an integer number of electrons.
$n$
Add $n/1000$ electrons to the system.

RECOMMENDATION:

Use only if trying to generate $E(N)$ plots. If $$, a fraction of an
electron is removed from the system.

FRAGMO_GUESS_MODE

Decide what to do regarding the FRAGMO guess in the present job
(for gen_scfman only)

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
Spawn fragment jobs sequentially and collect the results as the
FRAGMO guess at the end.
1
Generate fragment inputs in folders “FrgX" under the scratch directory of
the present job
and then terminate. Users can then take advantage of a queuing system to run these jobs
simultaneously using “FrgX" as their scratch folders (should be handled
with scripting).
2
Read in the available fragment data.

RECOMMENDATION:

Consider using “1" if the fragment calculations are evenly expensive. Use
“2" when FRAGMO guess is pre-computed.

FRGM_LPCORR

Specifies a