# C.4 Alphabetical Listing of $rem Variables (May 16, 2021) BASIS Specifies the electronic basis sets to be used. TYPE: STRING DEFAULT: No default basis set OPTIONS: General, Gen User defined ($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${}_{s}=-{{1}\over{2}}$).
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0 Do not look for any IP/$\alpha$ states.
OPTIONS:
$[i,j,k\ldots]$ 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${}_{s}$=${{1}\over{2}}$, default for CVS-IP).
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0 Do not look for any IP/$\beta$ states.
OPTIONS:
$[i,j,k\ldots]$ 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 $rem variable “METHOD RECOMMENDATION: A mean-field method (pure or hybrid density functional) should be chosen. ESP_EFIELD Triggers the calculation of ESP and/or E-field at nuclear positions or on a given grid of points TYPE: INTEGER DEFAULT: 0 OPTIONS: 0 Compute ESP only 1 Compute both ESP and electric field 2 Compute electric field only RECOMMENDATION: None EX_EDA Perform an ALMO-EDA calculation with one or more fragments excited. TYPE: BOOLEAN DEFAULT: FALSE OPTIONS: TRUE Perform EDA with excited-state molecule(s) taken into account. FALSE RECOMMENDATION: None FODFT_DONOR Specify the donor fragment in FODFT calculation TYPE: INTEGER DEFAULT: 1 OPTIONS: 1 First fragment as donor 2 Second fragment as donor RECOMMENDATION: With FODFT_METHOD = 1, the charged fragment needs to be the donor fragment FODFT_METHOD Specify the flavor of FODFT method TYPE: INTEGER DEFAULT: 1 OPTIONS: 1 FODFT($\mathrm{2n-1}$)@$D^{+}A$ (HT) / FODFT($\mathrm{2n+1}$)@$D^{-}A$ (ET) 2 FODFT($\mathrm{2n}$)@$DA$ 3 FODFT($\mathrm{2n-1}$)@$DA$ (HT) / FODFT($\mathrm{2n+1}$)@$D^{-}A^{-}$ (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, 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 $\bar{\mathbf{F}}_{da}$ 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, $Y=2N^{2}$.
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.

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 $10^{-\mathrm{NEO\_BASIS\_LIN\_DEP\_THRESH}}$.
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 $10^{-\mathrm{NEO\_E\_CONV}}$.
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 $10^{-\mathrm{NEO\_N\_SCF\_CONVERGENCE}}$.
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 $10^{-\mathrm{SCF\_CONVERGENCE}}$. 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.

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 $10^{-\mbox{{\small THRESH\_DP\_SWITCH}}}$ 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 $10^{-\mbox{{\small THRESH\_LS\_SWITCH}}}$ 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 $occupied information (see Section 4.4 on initial guesses). VFB_CTA Use the Variational Forward-Backward (VFB) approach to obtain “one-way” CT PESs. TYPE: STRING DEFAULT: NONE OPTIONS: FORWARD Allow 1$\rightarrow$2 CT only (1 and 2 are two fragments). BACKWARD Allow 2$\rightarrow$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, $Y=2N^{2}$. 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

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.

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: $n\leq 12$ 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: $n\leq 14$ 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 $\Sigma(4+)$ 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 $\Sigma(4)$ 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 $\Sigma(4+)$ procedure RECOMMENDATION: In case of IP-ADC(3) calculations, employing the $\Sigma(4+)$ 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 $\hat{r}^{2}$ 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 ($\geq 1000$) 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. $1\leq n\leq\mbox{{\small AIMD\_STEPS}}$ 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: $1\leq n\leq\mbox{{\small AIMD\_STEPS}}$ 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. $1\leq n\leq\mbox{{\small AIMD\_STEPS}}$ 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 $N<0$ search from the top determinants whose cumulative weight in the wavefunction corresponds to $1-2^{N}$ RECOMMENDATION: Using a dynamically determined value ($N<0$) 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

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:
$n>\text{\mbox{{\small CAP\_X}}}$ 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:
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 $\tilde{\sigma}$-intermediates for canonical and $\sigma$-intermediates for RI/CD response calculations). 2 Use $\sigma$-intermediates for 2PA response equation calculations. 3 Use $\tilde{\sigma}$-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 $\langle S^{2}\rangle$. 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 $\langle S^{2}\rangle$. The variable CC_EOM_PROP must be also set to TRUE. Alternatively, CC_CALC_SSQ can be used to request $\langle S^{2}\rangle$ 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 $\langle X^{2}\rangle$, $\langle Y^{2}\rangle$, and $\langle Z^{2}\rangle$ of electron density, and the total $\langle R^{2}\rangle=\langle X^{2}\rangle+\langle Y^{2}\rangle+\langle Z^{2}\rangle$ (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 $\langle S^{2}\rangle$. 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 $\langle S^{2}\rangle$. 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 $\langle X^{2}\rangle$, $\langle Y^{2}\rangle$, and $\langle Z^{2}\rangle$ of electron density, and the total $\langle R^{2}\rangle=\langle X^{2}\rangle+\langle Y^{2}\rangle+\langle Z^{2}\rangle$ (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 $10^{-\mathrm{CDFTCI\_SVD\_THRESH}}$ 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, , 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.

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.

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.
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 $10^{-\mathrm{CIS\_CONVERGENCE}}$ 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 ($\leq$ 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:
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 $\langle\hat{S}^{2}\rangle$ threshold to $n/100$
RECOMMENDATION:
For the default case, states with $\langle\hat{S}^{2}\rangle>1.2$ 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.  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. . 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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 $\Delta$ 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–$N_{\rm atoms}$ 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_A1 The nonlinear parameter $\alpha_{1}$ in Eqs. (5.29), (5.30), (5.31), and (5.32). Used in DFT-D3(BJ), DFT-D3(CSO), DFT-D3M(0), DFT-D3M(BJ), and DFT-D3(op). TYPE: INTEGER DEFAULT: 100000 OPTIONS: $n$ Corresponding to $\alpha_{1}=n/100000$. RECOMMENDATION: NONE DFT_D3_A2 The nonlinear parameter $\alpha_{2}$ in Eqs. (5.29) and (5.32). Used in DFT-D3(BJ), DFT-D3M(BJ), and DFT-D3(op). TYPE: INTEGER DEFAULT: 100000 OPTIONS: $n$ Corresponding to $\alpha_{2}=n/100000$. 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_RS6 The nonlinear parameter $s_{r,6}$ in Eqs. (5.28) and Eq. (5.31). Used in DFT-D3(0) and DFT-D3M(0). TYPE: INTEGER DEFAULT: 100000 OPTIONS: $n$ Corresponding to $s_{r,6}=n/100000$. RECOMMENDATION: NONE DFT_D3_RS8 The nonlinear parameter $s_{r,8}$ in Eqs. (5.28) and Eq. (5.31). Used in DFT-D3(0) and DFT-D3M(0). TYPE: INTEGER DEFAULT: 100000 OPTIONS: $n$ Corresponding to $s_{r,8}=n/100000$. 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 EMPIRICAL_CHG DFT-CHG dispersion correction from Chai and Head-Gordon 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. D3_BJ DFT-D3(BJ) dispersion correction from Grimme et al. D3_CSO DFT-D3(CSO) dispersion correction from Schröder et al. D3_ZEROM DFT-D3M(0) dispersion correction from Smith et al. D3_BJM DFT-D3M(BJ) dispersion correction from Smith et al. D3_OP DFT-D3(op) dispersion correction from Witte et al. D3 Automatically select the “best” available D3 dispersion correction D4 DFT-D4 dispersion correction from Caldeweyher et al. ,, 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $[i,j,k\ldots]$ 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: $n<10$ 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: $n<10$ 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 $[n_{1},n_{2},...]$ 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 $[n_{1},n_{2},...]$ 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 $[n_{1},n_{2},...]$ 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 $[n_{1},n_{2},...]$ 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. $\mu<10^{2}$ 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 $[n_{1},n_{2},...]$ 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 $[n_{1},n_{2},...]$ 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 $[n_{1},n_{2},...]$ 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 $[n_{1},n_{2},...]$ 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 $E_{\rm est}\pm n\times 10^{-6}\;E_{h}$.
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 $n<0$, 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 c