C.5.1 Overview

BASIS
       Specifies the electronic basis sets to be used.
TYPE:
       STRING
DEFAULT:
       No default basis set
OPTIONS:
       General, Gen User defined ($basis keyword required). Symbol Use standard basis sets as per Chapter 8. Mixed Use a mixture of basis sets (see Chapter 8).
RECOMMENDATION:
       Consult literature and reviews to aid your selection.

CONCENTRIC_REF_BASIS
       Specify the projection basis (PB) in the concentric localization procedure
TYPE:
       STRING
DEFAULT:
       NONE
OPTIONS:
       Parsed in the same way as BASIS; if unspecified, the working basis (WB) will be used as PB.
RECOMMENDATION:
       WB is usually a good choice; a smaller basis can chosen with caution to further reduce the computational cost.

CONCENTRIC_VIRTS_ZETA
       Specify the size of the truncated virtual space
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       $m$ The total number of the CL-truncated virtuals is $m\times n_{\text{occ}}^{\text{active}}$
RECOMMENDATION:
       Use the default; set it to a larger value if higher accuracy is requested.

CONCENTRIC_VIRTS
       Use the concentric localization (CL) scheme to truncate the virtual space
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE Use the CL scheme to truncate the virtual space FALSE Leave the virtual space untruncated
RECOMMENDATION:
       Use CL truncation for WFT-in-DFT calculations.

CVS_IP_ALPHA
       Sets the number of ionized target states derived by removing $\alpha$ electron (M${}_s=-\frac{1}{2}$).
TYPE:
       INTEGER/INTEGER ARRAY
DEFAULT:
       0 Do not look for any IP/$\alpha$ states.
OPTIONS:
       $[i,j,k\mathrm{\dots }]$ Find $i$ ionized states in the first irrep, $j$ states in the second irrep etc.
RECOMMENDATION:
       None

CVS_IP_BETA
       Sets the number of ionized target states derived by removing $\beta$ electron (M${}_s$=$\frac{1}{2}$, default for CVS-IP).
TYPE:
       INTEGER/INTEGER ARRAY
DEFAULT:
       0 Do not look for any IP/$\beta$ states.
OPTIONS:
       $[i,j,k\mathrm{\dots }]$ Find $i$ ionized states in the first irrep, $j$ states in the second irrep etc.
RECOMMENDATION:
       None

CVS_IP_STATES
       Sets the number of core-ionized states to find. By default, $\beta$ electron will be removed.
TYPE:
       INTEGER/INTEGER ARRAY
DEFAULT:
       0 Do not look for any IP states.
OPTIONS:
       [i,j,k…] Find $i$ ionized states in the first irrep, $j$ states in the second irrep etc.
RECOMMENDATION:
       None

DIRECT_DIAG
       Perform direct diagonalization to obtain all the NEO excitation energies.
TYPE:
       INTEGER
DEFAULT:
       0 Use Davidson algorithm.
OPTIONS:
       1 Do the direct diagonalization. 0 Use Davidson algorithm.
RECOMMENDATION:
       Only use this option when Davidson solutions are not stable.

DISTORT
       Specifies whether to apply pressure or external force to a chemical system
TYPE:
       LOGICAL
DEFAULT:
       False
OPTIONS:
       False Do not use pressure or force True Use pressure or force
RECOMMENDATION:
       Set to true to apply pressure or force.

EDA2_MOM
       Perform ALMO-EDA calculation with non-aufbau electronic configurations using MOM
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       FALSE Standard ALMO-EDA calculation TRUE ALMO-EDA for non-aufbau states
RECOMMENDATION:
       None

EDA_ALIGN_FRGM_SPIN
       Turn on the fragment spin alignment procedure
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not performed the spin alignment procedure (turned on by default in unrestricted cases) 1 Perform fragment spin alignment; use GDM for the polarization step preceding the MOM calculations 2 Perform fragment spin alignment; use GDM and perform stability analysis for the polarization step
RECOMMENDATION:
       Use 1 or 2 when the radical is of highly symmetric structure

EDA_NOCV
       Perform the NOCV analysis and plot the significant NOCVs
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not perform NOCV analysis 1 Plot NOCV pair contributions to density deformation 2 Plot both NOCV pair contribution to density deformation and NOCV orbitals
RECOMMENDATION:
       None

EDA_PLOT_DIFF_DEN
       Plot changes in electron density due to POL and CT
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       FALSE Do not make EDD plots TRUE Make EDD plots
RECOMMENDATION:
       None

EIGSLV_METH
       Control the method for solving the ALMO-CIS eigen-equation
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Explicitly build the Hamiltonian then diagonalize (full-spectrum). 1 Use the Davidson method (currently only available for restricted cases).
RECOMMENDATION:
       None

ENV_METHOD
       Specify the low-level theory in a projection-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

FIXING_V_EMBED
       Invoke the linearized approximation for the energy functional used for embedding calculations
TYPE:
       BOOLEAN
DEFAULT:
       TRUE
OPTIONS:
       TRUE Use the linearized approximation for energy functional [Eq. (11.99)] FALSE Use the original energy functional [Eq. (11.93)]
RECOMMENDATION:
       Use the default to achieve savings in computational costs

FODFT_DONOR
       Specify the donor fragment in FODFT calculation
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       1 First fragment as donor 2 Second fragment as donor
RECOMMENDATION:
       With FODFT_METHOD = 1, the charged fragment needs to be the donor fragment

FODFT_METHOD
       Specify the flavor of FODFT method
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       1 FODFT($2\mathrm{n}-1$)@$D^{+}A$ (HT) / FODFT($2\mathrm{n}+1$)@$D^{-}A$ (ET) 2 FODFT($2\mathrm{n}$)@$DA$ 3 FODFT($2\mathrm{n}-1$)@$DA$ (HT) / FODFT($2\mathrm{n}+1$)@$D^{-}{A}^{-}$ (ET)
RECOMMENDATION:
       The default approach shows the best overall performance

FRAG_DIABAT_DOHT
       Specify whether hole or electron transfer is considered
TYPE:
       BOOLEAN
DEFAULT:
       TRUE
OPTIONS:
       TRUE Do hole transfer FALSE Do electron transfer
RECOMMENDATION:
       Need to be specified for POD and FODFT calculations

FRAG_DIABAT_METHOD
       Specify fragment based diabatization method
TYPE:
       STRING
DEFAULT:
       NONE
OPTIONS:
       ALMO_MSDFT Perform ALMO(MSDFT) diabatization POD Perform projection operator diabatization (the original method) POD2_L Perform POD2 with Löwdin orthogonalization POD2_GS Perform POD2 with Grad-Schmidt orthogonalization ESID The energy-split-in-dimer method,¹¹⁴³ which is equivalent to the FMO approach introduced in Section 10.14.2.5 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 $\ge 1$ Print additional details
RECOMMENDATION:
       Use the default unless debug information is needed

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 projection-based embedding calculation using the implementation based onGEN_SCFMAN
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE Perform a projection-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.

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 5.3.5.;
RECOMMENDATION:
       In general, consult the literature to guide your selection. Our recommendations for DFT are indicated in bold in Section 5.3.5.

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.⁶⁰

MSDFT_METHOD
       Specify the scheme for ALMO(MSDFT)
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       1 The original MSDFT scheme [Eq. (10.134)] 2 The ALMO(MSDFT2) approach [Eq. (10.137)]
RECOMMENDATION:
       Use the default method. Note that the method will be automatically reset to 1 if a meta-GGA functional is requested.

MSDFT_PINV_THRESH
       Set the threshold for pseudo-inverse of the interstate overlap
TYPE:
       INTEGER
DEFAULT:
       4
OPTIONS:
       $n$ Set the threshold to 10${}^{-n}$
RECOMMENDATION:
       Use the default value

NDAMP
       Determine the mixing coefficient. $\alpha$ = NDAMP/100.
TYPE:
       INTEGER
DEFAULT:
       75
OPTIONS:
       User-defined. Integers between 0 and 100.
RECOMMENDATION:
       Increase NDAMP if strong fluctuations happen during the SCF process.

NEO_BASIS_LIN_DEP_THRESH
       This keyword is used to set the liner dependency threshold for nuclear basis sets. It is defined as ${10}^{-\mathrm{NEO}\mathrm{\_}\mathrm{BASIS}\mathrm{\_}\mathrm{LIN}\mathrm{\_}\mathrm{DEP}\mathrm{\_}\mathrm{THRESH}}$.
TYPE:
       DOUBLE
DEFAULT:
       5.0
OPTIONS:
       User-defined
RECOMMENDATION:
       No recommendation.

NEO_EPC
       Specifies the electron-proton correlation functional.
TYPE:
       STRING
DEFAULT:
       No default
OPTIONS:
       NAME Use NEO_EPC = NAME, where NAME can be either epc172 or epc19.
RECOMMENDATION:
       Consult the NEO literature to guide your selection.

NEO_E_CONV
       Energy convergence criteria in the NEO-SCF calculations so that the difference in energy between electronic and protonic iterations is less than ${10}^{-\mathrm{NEO}\mathrm{\_}\mathrm{E}\mathrm{\_}\mathrm{CONV}}$.
TYPE:
       INTEGER
DEFAULT:
       8
OPTIONS:
       User-defined
RECOMMENDATION:
       Tighter criteria for geometry optimization are recommended.

NEO_ISOTOPE
       Enable calculations of different types of isotopes. Only one type of isotope is allowed at present.
TYPE:
       INTEGER
DEFAULT:
       1 Default is the proton isotope.
OPTIONS:
       1 This NEO calculation is using proton isotope. 2 This NEO calculation is using deuterium isotope. 3 This NEO calculation is using tritium isotope.
RECOMMENDATION:
       Refer to the NEO literature for the best performance on the isotope effects calculations.

NEO_N_SCF_CONVERGENCE
       NEO-SCF is considered converged when the nuclear wave function error is less that ${10}^{-\mathrm{NEO}\mathrm{\_}\mathrm{N}\mathrm{\_}\mathrm{SCF}\mathrm{\_}\mathrm{CONVERGENCE}}$.
TYPE:
       INTEGER
DEFAULT:
       7
OPTIONS:
       User-defined
RECOMMENDATION:
       None.

NEO_PURECART
       This keyword is used to specify Cartesian or spherical Gaussians for nuclear basis functions.
TYPE:
       INTEGER
DEFAULT:
       2222
OPTIONS:
       User-defined
RECOMMENDATION:
       Default are Cartesian Gaussians. 1111 would define spherical Gaussians similar to keyword PURECART. Current NEO calculations do not support Cartesian electronic or nuclear basis sets with h angular momentum.

NEO_VPP
       Remove $J-K$ terms from the nuclear Fock matrix and the corresponding kernel terms for NEO excited state methods for the case of one quantum proton.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       1 Enable this option. 0 Disable this option.
RECOMMENDATION:
       Use this only in the case of one quantum hydrogen.

NEO
       Enable a NEO-SCF calculation.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE Enable a NEO-SCF calculation. FALSE Disable a NEO-SCF calculation.
RECOMMENDATION:
       Set to TRUE if desired.

POD_MULTI_PAIRS
       Calculate the couplings between multiple pairs of donor and acceptor orbitals in POD
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE Calculate the couplings between multiple pairs of orbitals FALSE Only calculate the D(HOMO)–A(HOMO) coupling (for HT) or D(LUMO)–A(LUMO) coupling (for ET)
RECOMMENDATION:
       None

POD_WINDOW
       Specify the number of donor and acceptor orbitals when couplings between multiple pairs are requested
TYPE:
       INTEGER
DEFAULT:
       5
OPTIONS:
       $n$ Including $n$ frontier occupied orbitals (from $\mathrm{HOMO}-n+1$ to HOMO) and $n$ frontier virtual orbitals (from LUMO to $\mathrm{LUMO}+n-1$) for both donor and acceptor
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

SCFMI_MOM
       Perform an SCFMI calculation with non-aufbau electronic configurations using MOM
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       FALSE Standard SCFMI calculation TRUE SCFMI calculation with MOM
RECOMMENDATION:
       None

SCF_ALGORITHM
       Algorithm used for converging the SCF.
TYPE:
       STRING
DEFAULT:
       DIIS Pulay DIIS.
OPTIONS:
       DIIS Pulay DIIS. DM Direct minimizer. DIIS_DM Uses DIIS initially, switching to direct minimizer for later iterations (See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES). DIIS_GDM Use DIIS and then later switch to geometric direct minimization (See THRESH_DIIS_SWITCH, MAX_DIIS_CYCLES). GDM Geometric Direct Minimization. RCA Relaxed constraint algorithm RCA_DIIS Use RCA initially, switching to DIIS for later iterations (see THRESH_RCA_SWITCH and MAX_RCA_CYCLES described later in this chapter) ROOTHAAN Roothaan repeated diagonalization.
RECOMMENDATION:
       In the NEO methods, the GDM procedure is recommended.

SCF_CONVERGENCE
       NEO-SCF is considered converged when the electronic wave function error is less that ${10}^{-\mathrm{SCF}\mathrm{\_}\mathrm{CONVERGENCE}}$. Adjust the value of THRESH at the same time. (Starting with Q-Chem 3.0, the DIIS error is measured by the maximum error rather than the RMS error as in earlier versions.)
TYPE:
       INTEGER
DEFAULT:
       5 For single point energy calculations. 8 For geometry optimizations.
OPTIONS:
       User-defined
RECOMMENDATION:
       None.

SET_CISGUES
       Controls how to generate the initial guess excitation vectors in CIS/TDA/RPA calculations.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Generate N (no. of roots requested) occupied$\to$virtual single orbital transitions according to their orbital energy difference order (from low to high). This is the common scenario. 1 Generate N-1 occupied$\to$virtual single orbital transitions according to their orbital energy difference order (from low to high), and generate another guess excitation vector consist of all the remaining single orbital transitions in the occupied$\to$virtual transition space with equal weights. 2 Generate N occupied/virtual single orbital transitions according to their orbital energy difference order (from low to high), and generate one more guess excitation vector consist of all the remaining single orbital transitions in the occupied$\to$virtual transition space with equal weights.
RECOMMENDATION:
       The default setting should work for most of the cases. However, when the no. of roots is small, in some CIS/TDA/RPA calculations low energy excited states could be missing. The options SET_CISGUES = 1 or 2 may remedy this root missing issue by sampling more vectors in the transition space. Setting SET_CISGUES = 1 or 2 may take more cycles to converge in the Davidson iteration, but the results are expected to be more reliable. Currently SET_CISGUES = 1 or 2 are not supported in SF-XCIS calculations. Setting TRNSS = TRUE also disables the setting of SET_CISGUES.

SET_ROOTS
       Sets the number of NEO excited state roots to find by Davidson or display the number of roots obtained by direct diagonalization.
TYPE:
       INTEGER
DEFAULT:
       0 Do not look for any excited states.
OPTIONS:
       $n$ $n>0$ Looks for $n$ NEO excited states.
RECOMMENDATION:
       None

SET_RPA
       Do a NEO-TDDFT or NEO-TDHF calculation.
TYPE:
       LOGICAL/INTEGER
DEFAULT:
       FALSE
OPTIONS:
       FALSE Do a NEO-TDA or NEO-CIS calculation. TRUE Do a NEO-TDDFT or NEO-TDHF calculation.
RECOMMENDATION:
       Consult the NEO literature to guide your selection.

SPADE_PARTITION
       Use the SPADE approach to determine the initial set of embedded (active) orbitals
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE Use SPADE to partition the occupied space FALSE Use the Pipek-Mezey localization + Mulliken population to assign occupied orbitals
RECOMMENDATION:
       Use SPADE if a significant gap in the spectrum of singular values can be detected.

THRESH_DP_SWITCH
       The threshold for turning off damping in SCF iterations is ${10}^{-\text{THRESH\_DP\_SWITCH}}$ when SCF_ALGORITHM is set to DP_DIIS or DP_GDM. See also MAX_DP_CYCLES.
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       User-defined.
RECOMMENDATION:
       None

THRESH_LS_SWITCH
       The threshold for turning off level-shifting in DIIS is ${10}^{-\text{THRESH\_LS\_SWITCH}}$ when SCF_ALGORITHM is set to LS_DIIS. See also MAX_LS_CYCLES.
TYPE:
       INTEGER
DEFAULT:
       4
OPTIONS:
       User-defined.
RECOMMENDATION:
       None

UNRESTRICTED
       Controls the use of restricted or unrestricted orbitals.
TYPE:
       LOGICAL
DEFAULT:
       FALSE Closed-shell systems. TRUE Open-shell systems.
OPTIONS:
       FALSE Constrain the spatial part of the alpha and beta orbitals to be the same. TRUE Do not Constrain the spatial part of the alpha and beta orbitals.
RECOMMENDATION:
       The ROHF method is not available. Note that for unrestricted calculations on systems with an even number of electrons it is usually necessary to break $\alpha$/$\beta$ symmetry in the initial guess, by using SCF_GUESS_MIX or providing $occupied information (see Section 4.4 on initial guesses).

VFB_CTA
       Use the Variational Forward-Backward (VFB) approach to obtain “one-way” CT PESs.
TYPE:
       STRING
DEFAULT:
       NONE
OPTIONS:
       FORWARD Allow 1$\to$2 CT only (1 and 2 are two fragments). BACKWARD Allow 2$\to$1 CT only.
RECOMMENDATION:
       None

XC_GRID
       Specifies the type of grid to use for DFT calculations.
TYPE:
       INTEGER
DEFAULT:
       Functional-dependent; see Table 5.3.
OPTIONS:
       0 Use SG-0 for H, C, N, and O; SG-1 for all other atoms. $n$ Use SG-$n$ for all atoms, $n=1,2$, or 3 $XY$ A string of two six-digit integers $X$ and $Y$, where $X$ is the number of radial points and $Y$ is the number of angular points where possible numbers of Lebedev angular points, which must be an allowed value from Table 5.2 in Section 5.5. $-XY$ Similar format for Gauss-Legendre grids, with the six-digit integer $X$ corresponding to the number of radial points and the six-digit integer $Y$ providing the number of Gauss-Legendre angular points, $Y=2N^2$.
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 specified using SCF_SAVEMINIMA = $n$. 4 Generate all CAS excitations from each reference determinant, where the active orbitals are specified using the $active_orbitals input section.
RECOMMENDATION:
       By default, these multiple determinants are optimized at the SCF level before running NOCI. This behavior 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 SCF_READMINIMA.

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.

REL_X2C_FD_DISPLACEMENT
       Controls finite difference step for calulating W
TYPE:
       INTEGER
DEFAULT:
       100
OPTIONS:
       $n$ Set finite difference step to $n\times {10}^{-6}$
RECOMMENDATION:
       None

REL_X2C
       Enables X2C scalar relativistic calculation
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Perform a regular, non-relativistic SCF calculation 1 Perform a scalar relativistic X2C calculation
RECOMMENDATION:
       Set to 1 if a scalar relativistic X2C calculation is desired.

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.

EDA_COVP_THRESH
       Specifies the significance above which the COVPs will be saved
TYPE:
       INTEGER
DEFAULT:
       5
OPTIONS:
       $N$ COVPs that accounts for more than $N$% of the fragment-wise energy or charge transfer will be saved
RECOMMENDATION:
       None

EDA_PCT_A
       Perform perturbative CT analysis
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not perform perturbative CT analysis 1 Perform perturbative CT analysis
RECOMMENDATION:
       Set to 1 to perform perturbative CT analysis

EDA_SAVE_COVP
       Save significant COVPs or not
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not save significant COVPs 1 Save significant COVPs
RECOMMENDATION:
       To save the COVPs as an fchk file, GUI = 2 also has to be set

EDA_VCT_A
       Perform non-perturbative CT analysis
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not perform non-perturbative CT analysis 1 Perform non-perturbative CT analysis.
RECOMMENDATION:
       Set to 1 to perform non-perturbative CT analysis

GEN_SCFMAN_EDA2
       Perform ALMO-EDA calculations using the GEN_SCFMAN_EDA2 driver (differing from jobs with EDA2 $>$ 0)
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not use the new ALMO-EDA framework 1 Use the new ALMO-EDA framework
RECOMMENDATION:
       Set to 1 to perform non-perturbative CT analysis

PLOT_ALMO_FRZ
       Plot ALMOs at the frozen stage of EDA2 calculations
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       FALSE Do not plot frozen ALMOs TRUE Plot frozen ALMOs
RECOMMENDATION:
       None

PLOT_ALMO_POL
       Plot ALMOs after the polarization calculation
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       FALSE Do not plot polarized ALMOs TRUE Plot polarized ALMOs
RECOMMENDATION:
       None

FDIFF_STEPSIZE
       Displacement used for calculating derivatives by finite difference.
TYPE:
       INTEGER
DEFAULT:
       1 Corresponding to $1.88973\times {10}^{-5}$ a.u.
OPTIONS:
       $n$ Use a step size of $n$ times the default value.
RECOMMENDATION:
       Use the default unless problems arise.

RESPONSE_POLAR
       Control the use of analytic or numerical polarizabilities.
TYPE:
       INTEGER
DEFAULT:
       0 or $-$1 = 0 for HF or DFT, $-$1 for all other methods
OPTIONS:
       0 Perform an analytic polarizability calculation. $-$1 Perform a numeric polarizability calculation even when analytic 2nd derivatives are available.
RECOMMENDATION:
       None

ADC_CAP
       Controls the type of CAP/ADC calculation to be performed.
TYPE:
       INTEGER
DEFAULT:
       0 Do not perform a CAP/ADC calculation.
OPTIONS:
       1 Perform a subspace-projected CAP/ADC calculation.
RECOMMENDATION:
       Set to 1 for the computation of CAP/ADC subspace projections.

ADC_CVS
       Activates the use of the CVS approximation for the calculation of CVS-ADC core-excited states.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Activates the CVS approximation. FALSE Do not compute core-excited states using the CVS approximation.
RECOMMENDATION:
       Set to TRUE, if to obtain core-excited states for the simulation of X-ray absorption spectra. In the case of TRUE, the $rem variable CC_REST_OCC has to be defined as well.

ADC_C_C
       Set the spin-opposite scaling parameter $c_c$ for the ADC(2) calculation. The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.
TYPE:
       INTEGER
DEFAULT:
       1170 Optimized value $c_c=1.17$ for ADC(2)-s or 1000 $c_c=1.0$ for ADC(2)-x
OPTIONS:
       $n$ Corresponding to $n\cdot {10}^{-3}$
RECOMMENDATION:
       Use the default.

ADC_C_T
       Set the spin-opposite scaling parameter $c_T$ for an SOS-ADC(2) calculation. The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.
TYPE:
       INTEGER
DEFAULT:
       1300 Optimized value $c_T=1.3$.
OPTIONS:
       $n$ Corresponding to $n\cdot {10}^{-3}$
RECOMMENDATION:
       Use the default.

ADC_C_X
       Set the spin-opposite scaling parameter $c_x$ for the ADC(2)-x calculation. The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.
TYPE:
       INTEGER
DEFAULT:
       1300 Optimized value $c_x=0.9$ for ADC(2)-x.
OPTIONS:
       $n$ Corresponding to $n\cdot {10}^{-3}$
RECOMMENDATION:
       Use the default.

ADC_DAVIDSON_CONV
       Controls the convergence criterion of the Davidson procedure.
TYPE:
       INTEGER
DEFAULT:
       $6$ Corresponding to ${10}^{-6}$
OPTIONS:
       $n\le 12$ Corresponding to ${10}^{-n}$.
RECOMMENDATION:
       Use the default unless higher accuracy is required or convergence problems are encountered.

ADC_DAVIDSON_MAXITER
       Controls the maximum number of iterations of the Davidson procedure.
TYPE:
       INTEGER
DEFAULT:
       60
OPTIONS:
       $n$ Number of iterations
RECOMMENDATION:
       Use the default unless convergence problems are encountered.

ADC_DAVIDSON_MAXSUBSPACE
       Controls the maximum subspace size for the Davidson procedure.
TYPE:
       INTEGER
DEFAULT:
       $5\times$ the number of excited states to be calculated.
OPTIONS:
       $n$ User-defined integer.
RECOMMENDATION:
       Should be at least 2–4$\times$ the number of excited states to calculate. The larger the value the more disk space is required.

ADC_DAVIDSON_THRESH
       Controls the threshold for the norm of expansion vectors to be added during the Davidson procedure.
TYPE:
       INTEGER
DEFAULT:
       Twice the value of ADC_DAVIDSON_CONV, but at maximum ${10}^{-14}$.
OPTIONS:
       $n\le 14$ Corresponding to ${10}^{-n}$
RECOMMENDATION:
       Use the default unless convergence problems are encountered. The threshold value ${10}^{-n}$ should always be smaller than the convergence criterion ADC_DAVIDSON_CONV.

ADC_DENSITY_MAXITER
       When setting ADC_DENSITY_ORDER = 4, this keyword controls the maximum number of DIIS iterations carried out in the $\mathrm{\Sigma }(4+)$ procedure.
TYPE:
       INTEGER
DEFAULT:
       1000
OPTIONS:
       $n$ User-defined integer.
RECOMMENDATION:
       Use the default value.

ADC_DENSITY_ORDER
       Controls the order of the ground state density used for the computation of third-order ADC matrix elements (non-CVS methods only).
TYPE:
       INTEGER
DEFAULT:
       2 Use strict third-order ADC(3) schemes.
OPTIONS:
       3 Use a third-order ground state density computed from the IP-ADC(3) effective transition moments and the corresponding fourth order static self-energy according to the $\mathrm{\Sigma }(4)$ scheme 4 Use an improved third-order ground state density and the corresponding improved fourth-order static self-energy computed according to the self-consistent $\mathrm{\Sigma }(4+)$ procedure
RECOMMENDATION:
       In case of IP-ADC(3) calculations, employing the $\mathrm{\Sigma }(4+)$ scheme provides more accurate ionization potentials and ionized state dipole moments.

ADC_DIIS_ECONV
       Controls the convergence criterion for the excited state energy during DIIS.
TYPE:
       INTEGER
DEFAULT:
       6 Corresponding to ${10}^{-6}$
OPTIONS:
       $n$ Corresponding to ${10}^{-n}$
RECOMMENDATION:
       None

ADC_DIIS_MAXITER
       Controls the maximum number of DIIS iterations.
TYPE:
       INTEGER
DEFAULT:
       50
OPTIONS:
       $n$ User-defined integer.
RECOMMENDATION:
       Increase in case of slow convergence.

ADC_DIIS_RCONV
       Convergence criterion for the residual vector norm of the excited state during DIIS.
TYPE:
       INTEGER
DEFAULT:
       6 Corresponding to ${10}^{-6}$
OPTIONS:
       $n$ Corresponding to ${10}^{-n}$
RECOMMENDATION:
       None

ADC_DIIS_SIZE
       Controls the size of the DIIS subspace.
TYPE:
       INTEGER
DEFAULT:
       7
OPTIONS:
       $n$ User-defined integer
RECOMMENDATION:
       None

ADC_DIIS_START
       Controls the iteration step at which DIIS is turned on.
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       $n$ User-defined integer.
RECOMMENDATION:
       Set to a large number to switch off DIIS steps.

ADC_DIRECT
       For third-order ADC methods, this keyword controls if some large intermediate tensor contractions should be carried out in advance and the result saved in memory for later use or if these quantities should be evaluated directly whenever they are encountered.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Directly evaluate some $N^6$-scaling tensor contractions. This will reduce the memory requirement by $\sim$10 %. FALSE Precompute all possible $N^6$-scaling intermediates. This will speed up ADC(3) calculations considerably (by a factor of $\sim$3 in case of ADC(3) for $N$-electron excitations and somewhat less for IP- and EA-ADC(3)).
RECOMMENDATION:
       Use the default value unless memory is the bottleneck.

ADC_DO_DIIS
       Activates the use of the DIIS algorithm for the calculation of ADC(2) excited states.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Use DIIS algorithm. FALSE Do diagonalization using Davidson algorithm.
RECOMMENDATION:
       None.

ADC_DO_DYSON
       Controls if Dyson orbitals are output in case of IP- and EA-ADC calculations. This keyword only takes effect when used together with STATE_ANALYSIS = TRUE. See Section. 10.2.9 for further details.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Output Dyson orbitals as cube files. FALSE Do not output Dyson orbitals.
RECOMMENDATION:
       Set to TRUE if visualization of ionization/electron-attachment processes is desired.

ADC_NGUESS_DOUBLES
       Controls the number of excited state guess vectors which are double excitations, two-hole-one-particle ionizations and one-hole-two-particle electron-attachments in case of ADC, IP-ADC and EA-ADC, respectively.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       $n$ User-defined integer.
RECOMMENDATION:
      

ADC_NGUESS_SINGLES
       Controls the number of excited state guess vectors which are single excitations, one-hole ionizations and one-particle electron-attachments in case of ADC, IP-ADC and EA-ADC, respectively. If the number of requested excited states exceeds the total number of guess vectors (singles and doubles), this parameter is automatically adjusted, so that the number of guess vectors matches the number of requested excited states.
TYPE:
       INTEGER
DEFAULT:
       Equals to the number of excited states requested.
OPTIONS:
       $n$ User-defined integer.
RECOMMENDATION:
       Increase if there are convergence problems.

ADC_PRINT
       Controls the amount of printing during an ADC calculation.
TYPE:
       INTEGER
DEFAULT:
       1 Basic status information and results are printed.
OPTIONS:
       0 Quiet: almost only results are printed. 1 Normal: basic status information and results are printed. 2 Debug: more status information, extended information on timings. …
RECOMMENDATION:
       Use the default.

ADC_PROP_ES2ES
       Controls the calculation of transition properties between excited, ionized or electron-attached states (currently only transition dipole moments and oscillator strengths). For ADC for $N$-electron excitations, this keyword also controls the computation of two-photon absorption cross-sections of excited states using the sum-over-states expression.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Calculate state-to-state transition properties. FALSE Do not compute transition properties between excited, ionized or electron-attached states.
RECOMMENDATION:
       Set to TRUE, if state-to-state properties (ADC, IP-ADC, EA-ADC) or sum-over-states two-photon absorption cross-sections (only ADC) are required.

ADC_PROP_ES
       Controls the calculation of excited, ionized or electron-attached state properties (currently only dipole moments and ${\widehat{r}}^2$ expectation values).
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Calculate excited, ionized or electron-attached state properties. FALSE Do not compute state properties.
RECOMMENDATION:
       Set to TRUE, if properties are required.

ADC_PROP_TPA
       Controls the calculation of two-photon absorption cross-sections of excited states using matrix inversion techniques.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Calculate two-photon absorption cross-sections. FALSE Do not compute two-photon absorption cross-sections.
RECOMMENDATION:
       Set to TRUE, if to obtain two-photon absorption cross-sections.

ADC_STRICT_ISR
       Controls how second-order ground state contributions are treated in the calculation of second- and third-order IP- and EA-ADC state properties using the second-order ISR formalism.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Scale the second-order part of the ground state contribution to one-electron properties of ionized/electron-attached states by the one-hole/one-particle character of the respective states as implied by the strict ISR derivation. FALSE Use the full second-order ground state contribution for each ionized/electron-attached state property.
RECOMMENDATION:
       Use the default value. Both options are, however, valid second-order treatments of ionized/electron-attached state properties and should yield very similar results for states with predominant one-hole/one-particle chaaracter.

ADD_CHARGED_CAGE
       Add a point charge cage of a given radius and total charge.
TYPE:
       INTEGER
DEFAULT:
       0 No cage.
OPTIONS:
       0 No cage. 1 Dodecahedral cage. 2 Spherical cage.
RECOMMENDATION:
       Spherical cage is expected to yield more accurate results, especially for small radii.

ADIIS_INNER_CONV
       Convergence criterion for the ADIIS inner loops (L-BFGS optimization of Eq. 4.43)
TYPE:
       INTEGER
DEFAULT:
       12
OPTIONS:
       $n$ Using 10${}^{-n}$ as the convergence criterion for the ADIIS inner loops
RECOMMENDATION:
       Use the default

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.  1092, 1095, 620 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:
       Use if CT states are desired in the basis.

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 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 how many NTOs that are retained in the exciton-site basis states.
TYPE:
       INTEGER
DEFAULT:
       99
OPTIONS:
       $n$ Retain enough NTOs to recover $n$% of the norm of the original CIS or TDDFT vectors in Eq. (12.68).
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 thhe 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 the chunk to be computed.
RECOMMENDATION:
       Needs to be used with AIFDEM_SEGEND

AIFDEM_SINGFIS
       Include multi-exciton states in the AIFDEM basis.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Include multi-exciton states. FALSE Do not include multi-exciton states.
RECOMMENDATION:
       Use if multi-exciton states are desired in the basis. This option requires the use of AIFDEM_SEGSTART and AIFDEM_SEGEND in the $rem section.

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. 454 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. OLD Use the same initial velocities as the immediately preceding AIMD job. RESTART Use the final velocities from a previous AIMD job, reading them from disk.
RECOMMENDATION:
       This variable need only be specified in the event that velocities are not specified explicitly in a $velocity section.

AIMD_LANGEVIN_TIMESCALE
       Sets the timescale (strength) of the Langevin thermostat
TYPE:
       INTEGER
DEFAULT:
       none
OPTIONS:
       $n$ Thermostat timescale,asn $n$ fs
RECOMMENDATION:
       Smaller values (roughly 100) equate to tighter thermostats but may inhibit rapid sampling. Larger values ($\ge 1000$) allow for more rapid sampling but may take longer to reach thermal equilibrium.

AIMD_METHOD
       Selects an ab initio molecular dynamics algorithm.
TYPE:
       STRING
DEFAULT:
       BOMD
OPTIONS:
       BOMD Born-Oppenheimer molecular dynamics. CURVY Curvy-steps Extended Lagrangian molecular dynamics.
RECOMMENDATION:
       BOMD yields exact classical molecular dynamics, provided that the energy is tolerably conserved. ELMD is an approximation to exact classical dynamics whose validity should be tested for the properties of interest.

AIMD_MOMENTS
       Requests that multipole moments be output at each time step.
TYPE:
       INTEGER
DEFAULT:
       0 Do not output multipole moments.
OPTIONS:
       $n$ Output the first $n$ multipole moments.
RECOMMENDATION:
       None

AIMD_NUCL_DACF_POINTS
       Number of time points to use in the dipole auto-correlation function for an AIMD trajectory
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not compute dipole auto-correlation function. $1\le n\le \text{AIMD\_STEPS}$ Compute dipole auto-correlation function for last $n$ timesteps of the trajectory.
RECOMMENDATION:
       If the DACF is desired, set equal to AIMD_STEPS.

AIMD_NUCL_SAMPLE_RATE
       The rate at which sampling is performed for the velocity and/or dipole auto-correlation function(s). Specified as a multiple of steps; i.e., sampling every step is 1.
TYPE:
       INTEGER
DEFAULT:
       None.
OPTIONS:
       $1\le n\le \text{AIMD\_STEPS}$ Update the velocity/dipole auto-correlation function every $n$ steps.
RECOMMENDATION:
       Since the velocity and dipole moment are routinely calculated for ab initio methods, this variable should almost always be set to 1 when the VACF/DACF are desired.

AIMD_NUCL_VACF_POINTS
       Number of time points to use in the velocity auto-correlation function for an AIMD trajectory
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Do not compute velocity auto-correlation function. $1\le n\le \text{AIMD\_STEPS}$ Compute velocity auto-correlation function for last $n$ time steps of the trajectory.
RECOMMENDATION:
       If the VACF is desired, set equal to AIMD_STEPS.

AIMD_QCT_INITPOS
       Chooses the initial geometry in a QCT-MD simulation.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       $0$ Use the equilibrium geometry. $n$ Picks a random geometry according to the harmonic vibrational wave function. $-n$ Generates $n$ random geometries sampled from the harmonic vibrational wave function.
RECOMMENDATION:
       None.

AIMD_QCT_WHICH_TRAJECTORY
       Picks a set of vibrational quantum numbers from a random distribution.
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       $n$ Picks the $n$th set of random initial velocities. $-n$ Uses an average over $n$ random initial velocities.
RECOMMENDATION:
       Pick a positive number if you want the initial velocities to correspond to a particular set of vibrational occupation numbers and choose a different number for each of your trajectories. If initial velocities are desired that corresponds to an average over $n$ trajectories, pick a negative number.

AIMD_SHORT_TIME_STEP
       Specifies a shorter electronic time step for FSSH calculations.
TYPE:
       INTEGER
DEFAULT:
       TIME_STEP
OPTIONS:
       $n$ Specify an electronic time step duration of $n$/AIMD_TIME_STEP_CONVERSION a.u. If $n$ is less than the nuclear time step variable TIME_STEP, the electronic wave function will be integrated multiple times per nuclear time step, using a linear interpolation of nuclear quantities such as the energy gradient and derivative coupling. Note that $n$ must divide TIME_STEP evenly.
RECOMMENDATION:
       Make AIMD_SHORT_TIME_STEP as large as possible while keeping the trace of the density matrix close to unity during long simulations. Note that while specifying an appropriate duration for the electronic time step is essential for maintaining accurate wave function time evolution, the electronic-only time steps employ linear interpolation to estimate important quantities. Consequently, a short electronic time step is not a substitute for a reasonable nuclear time step.

AIMD_STEPS
       Specifies the requested number of molecular dynamics steps.
TYPE:
       INTEGER
DEFAULT:
       None.
OPTIONS:
       User-specified.
RECOMMENDATION:
       None.

AIMD_TEMP
       Specifies a temperature (in Kelvin) for Maxwell-Boltzmann velocity sampling.
TYPE:
       INTEGER
DEFAULT:
       None
OPTIONS:
       User-specified number of Kelvin.
RECOMMENDATION:
       This variable is only useful in conjunction with AIMD_INIT_VELOC = THERMAL. Note that the simulations are run at constant energy, rather than constant temperature, so the mean nuclear kinetic energy will fluctuate in the course of the simulation.

AIMD_THERMOSTAT
       Applies thermostatting to AIMD trajectories.
TYPE:
       INTEGER
DEFAULT:
       none
OPTIONS:
       LANGEVIN Stochastic, white-noise Langevin thermostat NOSE_HOOVER Time-reversible, Nosé-Hoovery chain thermostat
RECOMMENDATION:
       Use either thermostat for sampling the canonical (NVT) ensemble.

AIMD_TIME_STEP_CONVERSION
       Modifies the molecular dynamics time step to increase granularity.
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       $n$ The molecular dynamics time step is TIME_STEP/$n$ a.u.
RECOMMENDATION:
       None

AIRBED_ALPHA
       Sets the value of $\alpha$.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       $n$ Corresponding to $\alpha$ = $n/1000$
RECOMMENDATION:
       0 or -1200 for hBN surface

AIRBED
       Perform an AIRBED calculation.
TYPE:
       BOOLEAN
DEFAULT:
       False
OPTIONS:
       True Perform an AIRBED calculation. False Don’t perform an AIRBED calculation.
RECOMMENDATION:
       Set the $rem variable DFT_D to EMPIRICAL_GRIMME.

ANHAR_SEL
       Select a subset of normal modes for subsequent anharmonic frequency analysis.
TYPE:
       LOGICAL
DEFAULT:
       FALSE Use all normal modes
OPTIONS:
       TRUE Select subset of normal modes
RECOMMENDATION:
       None

ANHAR
       Performing various nuclear vibrational theory (TOSH, VPT2, VCI) calculations to obtain vibrational anharmonic frequencies.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Carry out the anharmonic frequency calculation. FALSE Do harmonic frequency calculation.
RECOMMENDATION:
       Since this calculation involves the third and fourth derivatives at the minimum of the potential energy surface, it is recommended that the GEOM_OPT_TOL_DISPLACEMENT, GEOM_OPT_TOL_GRADIENT and GEOM_OPT_TOL_ENERGY tolerances are set tighter. Note that VPT2 calculations may fail if the system involves accidental degenerate resonances. See the VCI $rem variable for more details about increasing the accuracy of anharmonic calculations.

ANTIBOND
       Triggers Antibond subroutine to generate antibonding orbitals after a converged SCF
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Does not localize the virtual space. 1 Localizes the virtual space, one antibonding for every bond. 2,3 Fill the virtual space with antibonding orbitals-like guesses. 4 Does Frozen Natural Orbitals and leaves them on scratch for future jobs or visualization.
RECOMMENDATION:
       None

ARI_R0
       Determines the value of the inner fitting radius (in Ångstroms)
TYPE:
       INTEGER
DEFAULT:
       4 A value of 4 Å will be added to the atomic van der Waals radius.
OPTIONS:
       $n$ User defined radius.
RECOMMENDATION:
       For some systems the default value may be too small and the calculation will become unstable.

ARI_R1
       Determines the value of the outer fitting radius (in Ångstroms)
TYPE:
       INTEGER
DEFAULT:
       5 A value of 5 Å will be added to the atomic van der Waals radius.
OPTIONS:
       $n$ User defined radius.
RECOMMENDATION:
       For some systems the default value may be too small and the calculation will become unstable. This value also determines, in part, the smoothness of the potential energy surface.

ARI
       Toggles the use of the atomic resolution-of-the-identity (ARI) approximation.
TYPE:
       LOGICAL
DEFAULT:
       FALSE ARI will not be used by default for an RI-JK calculation.
OPTIONS:
       TRUE Turn on ARI.
RECOMMENDATION:
       For large (especially 1D and 2D) molecules the approximation may yield significant improvements in Fock evaluation time.

ASCI_CDETS
       Specifies the number of determinants to search over during ASCI wavefunction growth steps.
TYPE:
       INTEGER
DEFAULT:
       -5
OPTIONS:
       $N>0$ search from the top $N$ determinants search from the top determinants whose cumulative weight in the wavefunction corresponds to $1-2^N$
RECOMMENDATION:
       Using a dynamically determined value () gives better results.

ASCI_DAVIDSON_GUESS
       Specifies the truncated CI guess used for ASCI’s Davidson solver.
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       $N$ Order of the truncated CI to solve explicitly ASCI Davidson guess.
RECOMMENDATION:
       Accurate excited states and rapid convergence of the ground state benefit from a good zero-order guess for the low energy spectrum. The default is often sufficient.

ASCI_DIAG
       Specifies the diagonalization procedure.
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       1 Davidson solver 2 Eigen sparse matrix solver
RECOMMENDATION:
       Use 2 for best trade-off of speed and memory usage. If memory usage becomes to great, switch to 1.

ASCI_NDETS
       Specifies the number of determinants to include in the ASCI wavefunction.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       $N$ for a wavefunction with $N$ determinants
RECOMMENDATION:
       Typical ASCI expansions range from 50,000 to 2,000,000 determinants depending on active space size, complexity of problem, and desired accuracy

ASCI_RESTART
       Specifies whether to initialize the ASCI wavefunction with the wf_data file.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE read CI coefficients from the wf_data file FALSE do not read the CI coefficients from disk
RECOMMENDATION:
      

ASCI_SKIP_PT2
       Specifies whether ASCI PT2 correction should be calculated.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       FALSE compute ASCI PT2 contribution TRUE do not compute ASCI PT2 contribution
RECOMMENDATION:
       The PT2 correction is essential to obtaining converged ASCI energies.

ASCI_SPIN_PURIFY
       Indicates whether or not the ASCI wavefunction should be augmented with missing determinants to ensure a spin-pure state.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE augment the wavefunction with determinants to ensure a spin eigenstate FALSE do not augment the wavefunction
RECOMMENDATION:
      

ASCI_USE_NAT_ORBS
       Specifies whether rotation to a natural orbital basis should be carried out between growth steps.
TYPE:
       BOOLEAN
DEFAULT:
       TRUE
OPTIONS:
       TRUE rotate to a natural orbital basis between growth wavefunction growth steps FALSE do not rotate to a natural orbital basis
RECOMMENDATION:
       Natural orbital rotations significantly improve the compactness and therefore accuracy of the ASCI wavefunction.

AUX_BASIS_CORR
       Sets the auxiliary basis set for RI-MP2 to be used or invokes RI-MP2 in case of double-hybrid DFT or MP2
TYPE:
       STRING
DEFAULT:
       No default auxiliary basis set
OPTIONS:
       General, Gen User-defined. As for BASIS Symbol Use standard auxiliary basis sets as in the table below Mixed Use a combination of different basis sets
RECOMMENDATION:
       Consult literature and Basis Set Exchange to aid your selection.

AUX_BASIS_J
       Sets the auxiliary basis set for RI-J to be used or invokes RI-J
TYPE:
       STRING
DEFAULT:
       No default auxiliary basis set
OPTIONS:
       General, Gen User-defined. As for BASIS Symbol Use standard auxiliary basis sets as in the table below Mixed Use a combination of different basis sets
RECOMMENDATION:
       Consult literature and Basis Set Exchange to aid your selection.

AUX_BASIS_K
       Sets the auxiliary basis set for RI-K or occ-RI-K to be used or invokes occ-RI-K
TYPE:
       STRING
DEFAULT:
       No default auxiliary basis set
OPTIONS:
       General, Gen User-defined. As for BASIS Symbol Use standard auxiliary basis sets as in the table below Mixed Use a combination of different basis sets
RECOMMENDATION:
       Consult literature and Basis Set Exchange to aid your selection.