# C.4 Alphabetical Listing of $rem Variables EDA_NOCV Perform the NOCV analysis and plot the significant NOCVs TYPE: BOOLEAN DEFAULT: FALSE OPTIONS: FALSE Do not perform NOCV analysis TRUE Perform NOCV analysis 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 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 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. 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 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. 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. 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.

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

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_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_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_NGUESS_DOUBLES Controls the number of excited state guess vectors which are double excitations. 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. 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: 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 states (currently only transition dipole moments and oscillator strengths), as well as 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 states. RECOMMENDATION: Set to TRUE, if state-to-state properties or sum-over-states two-photon absorption cross-sections are required. ADC_PROP_ES Controls the calculation of excited state properties (currently only dipole moments). TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Calculate excited 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. 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. 885, 888, 515 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_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 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. 367 for examples and discussion. 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 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.

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.

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 EMSL 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 EMSL 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 EMSL 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 EMSL Basis Set Exchange to aid your selection.

BASIS2
Sets the small basis set to use in basis set projection.
TYPE:
STRING
DEFAULT:
No second basis set default.
OPTIONS:
Symbol. Use standard basis sets as per Chapter 8. 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 (see Section 4.7).

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
Specifies the basis sets to be used.
TYPE:
STRING
DEFAULT:
No default basis set
OPTIONS:
General, Gen User defined ($basis keyword required). Symbol Use standard basis sets as per Chapter 8. Mixed Use a mixture of basis sets (see Chapter 8). RECOMMENDATION: Consult literature and reviews to aid your selection. BECKE_SHIFT Controls atomic cell shifting in determination of Becke weights. TYPE: STRING DEFAULT: UNSHIFTED OPTIONS: UNSHIFTED Use the original weighting scheme of Becke (bisection point). BRAGG_SLATER Use the empirically derived Bragg-Slater radii. UNIVERSAL_DENSITY Use the ab initio derived Pacios radii. RECOMMENDATION: If interested in the partitioning of the default atomic quadrature, use UNSHIFTED. If using for physical interpretation, choose BRAGG_SLATER or UNIVERSAL_DENSITY. BOYSCALC Specifies the Boys localized orbitals are to be calculated TYPE: INTEGER DEFAULT: 0 OPTIONS: 0 Do not perform localize the occupied space. 1 Allow core-valence mixing in Boys localization. 2 Localize core and valence separately. RECOMMENDATION: None BOYS_CIS_NUMSTATE Define how many states to mix with Boys localized diabatization. These states must be specified in the$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.
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, 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.

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 CTF Distributed-memory back-end for MPI jobs
RECOMMENDATION:
Use XM for large jobs with limited memory or when the performance of the default disk-based back-end is not satisfactory, CTF for MPI jobs

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 $abc\times 10^{-de}$, e.g., $2502$ corresponds to 0.25
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_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
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, 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_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_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. )

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_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, 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 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:
OPTIONS:
$n$ $10^{-n}$ convergence criterion.
RECOMMENDATION:
Use default

Convergence desired on the RMS gradient of the energy with respect to orbital rotation angles [$10^{-n}$].
TYPE:
INTEGER
DEFAULT:
OPTIONS:
$n$ $10^{-n}$ convergence criterion.
RECOMMENDATION:
Use default

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 for the EOM-CCSD target states will be calculated. By default, the transition dipole moment is calculated between the CCSD reference and the EOM-CCSD target states. In order to calculate transition dipole moment 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 if 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:
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:
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_CRASHONFAIL Whether the calculation should crash or not if the constraint iterations do not converge. TYPE: LOGICAL DEFAULT: TRUE OPTIONS: TRUE Crash if constraint iterations do not converge. FALSE Do not crash. RECOMMENDATION: Use the default. 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_POP Sets the charge partitioning scheme for cDFT in SAPT/cDFT TYPE: STRING DEFAULT: FBH OPTIONS: FBH Fragment-Based Hirshfeld partitioning BECKE Atomic Becke partitioning 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_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: 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,118, unless the cost is prohibitive, in which case a larger value can be selected. Note that this default value is set with the Cartesian grid in mind and not the Lebedev grid. In the Lebedev case, a larger value can typically be used. CHELPG_HA Sets the Lebedev grid to use for non-hydrogen atoms. TYPE: INTEGER DEFAULT: NONE OPTIONS: $N$ Corresponding to a number of points in a Lebedev grid (see Section 5.5.1. RECOMMENDATION: None. CHELPG_HEAD Sets the “head space”118 (radial extent) of the ChElPG grid. TYPE: INTEGER DEFAULT: 30 OPTIONS: $N$ Corresponding to a head space of $N/10$, in Å. RECOMMENDATION: Use the default, which is the value recommended by Breneman and Wiberg.118 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.559 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:
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) to hold a temporary array whose minimum size is $OV\times\mbox{{\small CIS\_N\_ROOTS}}$. For a large calculation, one has to specify a large value for MEM_STATIC, which is not recommended (see Chapter 2). Therefore, it is recommended to use dynamic memory for large calculations. CIS_GUESS_DISK_TYPE Determines the type of guesses to be read from disk TYPE: INTEGER DEFAULT: Nil OPTIONS: 0 Read triplets only 1 Read triplets and singlets 2 Read singlets only RECOMMENDATION: Must be specified if CIS_GUESS_DISK is TRUE. CIS_GUESS_DISK Read the CIS guess from disk (previous calculation). TYPE: LOGICAL DEFAULT: FALSE OPTIONS: FALSE Create a new guess. TRUE Read the guess from disk. RECOMMENDATION: Requires a guess from previous calculation. CIS_MOMENTS Controls calculation of excited-state (CIS or TDDFT) multipole moments TYPE: LOGICAL DEFAULT: FALSE OPTIONS: FALSE Do not calculate excited-state moments. TRUE Calculate moments for each excited state. RECOMMENDATION: Set to TRUE if excited-state moments are desired. (This is a trivial additional calculation.) The MULTIPOLE_ORDER controls how many multipole moments are printed. CIS_MULLIKEN Controls Mulliken and Löwdin population analyses for excited-state particle and hole density matrices. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: FALSE Do not perform particle/hole population analysis. TRUE Perform both Mulliken and Löwdin analysis of the particle and hole density matrices for each excited state. RECOMMENDATION: Set to TRUE if desired. This represents a trivial additional calculation. CIS_N_ROOTS Sets the number of excited state roots to find TYPE: INTEGER DEFAULT: 0 Do not look for any excited states OPTIONS: $n$ $n>0$ Looks for $n$ excited states RECOMMENDATION: None CIS_RELAXED_DENSITY Use the relaxed CIS density for attachment/detachment density analysis. 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_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
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 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_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.

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. 324).
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. (5.27), (5.28), (5.29), and (5.30). 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. (5.27) and (5.30). 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. (5.30). 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. (5.26) and Eq. (5.29). 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. (5.26) and Eq. (5.29). 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. (5.25). 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. (5.25). 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_D_A
Controls the strength of dispersion corrections in the Chai–Head-Gordon DFT-D scheme, Eq. (5.24).
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 Grimme331 EMPIRICAL_CHG DFT-CHG dispersion correction from Chai and Head-Gordon159 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.324 D3_BJ DFT-D3(BJ) dispersion correction from Grimme et al.326 D3_CSO DFT-D3(CSO) dispersion correction from Schröder et al.814 D3_ZEROM DFT-D3M(0) dispersion correction from Smith et al.850 D3_BJM DFT-D3M(BJ) dispersion correction from Smith et al.850 D3_OP DFT-D3(op) dispersion correction from Witte et al.996 D3 Automatically select the "best" available D3 dispersion correction
RECOMMENDATION:
Use the D3 option, which selects the empirical potential based on the density functional specified by the user.

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_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.

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
Sets the number of attached target states roots to find. By default, $\alpha$ electron will be attached (see EOM_EA_ALPHA).
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0 Do not look for any EA states.
OPTIONS:
$[i,j,k\ldots]$ Find $i$ EA states in the first irrep, $j$ states in the second irrep etc.
RECOMMENDATION:
None

ECP
Defines the effective core potential and associated basis set to be used
TYPE:
STRING
DEFAULT:
No ECP
OPTIONS:
General, Gen User defined. ($ecp keyword required) Symbol Use standard ECPs discussed above. RECOMMENDATION: ECPs are recommended for first row transition metals and heavier elements. Consul the reviews for more details. EDA2 Switch on EDA2 and specify the option set number. TYPE: INTEGER DEFAULT: 2 OPTIONS: 0 Do not run through EDA2. 1 Frozen energy decomposition + nDQ-FERF polarization (the standard EDA2 option) 2 Frozen energy decomposition + (AO-block-based) ALMO polarization (old scheme with the addition of frozen decomposition) 3 Frozen energy decomposition + oDQ-FERF polarization (NOT commonly used) 4 Frozen wave function relaxation + Frozen energy decomposition + nDQ-FERF polarization (NOT commonly used) 5 Frozen energy decomposition + polMO polarization (NOT commonly used). 10 No preset. Completely controlled by user’s$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_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

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, $\mu$ [Eq. (12.79) and (12.81)]. 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 Sets the number of attached target states derived by attaching $\alpha$ electron (M${}_{s}$=${{1}\over{2}}$, default in EOM-EA). TYPE: INTEGER/INTEGER ARRAY DEFAULT: 0 Do not look for any EA states. OPTIONS: $[i,j,k\ldots]$ Find $i$ EA states in the first irrep, $j$ states in the second irrep etc. RECOMMENDATION: None EOM_EA_BETA Sets the number of attached target states derived by attaching $\beta$ electron (M${}_{s}$=$-{{1}\over{2}}$, EA-SF). TYPE: INTEGER/INTEGER ARRAY DEFAULT: 0 Do not look for any EA states. OPTIONS: $[i,j,k\ldots]$ Find $i$ EA states in the first irrep, $j$ states in the second irrep etc. RECOMMENDATION: None 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 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 EOM_IP_BETA Sets the number of ionized target states derived by removing $\beta$ electron (M${}_{s}$=${{1}\over{2}}$, default for EOM-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 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 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_REF_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. 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_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:
$-2$ 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_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_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:
RECOMMENDATION:
Set the $rem variable FDE to TRUE to start a FDE-ADC 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 correction method performed after the locally-projected equations are converged.
TYPE:
STRING
DEFAULT:
NONE
OPTIONS:
ARS Approximate Roothaan-step perturbative correction. RS Single Roothaan-step perturbative correction. EXACT_SCF Full SCF variational correction. ARS_EXACT_SCF Both ARS and EXACT_SCF in a single job. RS_EXACT_SCF Both RS and EXACT_SCF in a single job.
RECOMMENDATION:
For large basis sets use ARS, use RS if ARS fails.

FRGM_METHOD
Specifies a locally-projected method.
TYPE:
STRING
DEFAULT:
NONE
OPTIONS:
STOLL Locally-projected SCF equations of Stoll are solved. GIA Locally-projected SCF equations of Gianinetti are solved. NOSCF_RS Single Roothaan-step correction to the FRAGMO initial guess. NOSCF_ARS Approximate single Roothaan-step correction to the FRAGMO initial guess. NOSCF_DRS Double Roothaan-step correction to the FRAGMO initial guess. NOSCF_RS_FOCK Non-converged SCF energy of the single Roothaan-step MOs.
RECOMMENDATION:
STOLL and GIA are for variational optimization of the ALMOs. NOSCF options are for computationally fast corrections of the FRAGMO initial guess.

FRZ_GEOM
Compute forces on the frozen PES.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
FALSE Do not compute forces on the frozen PES. TRUE Compute forces on the frozen PES.
RECOMMENDATION:
Set it to TRUE when optimized geometry or vibrational frequencies on the frozen PES are desired.

FRZ_ORTHO_DECOMP_CONV
Convergence criterion for the minimization problem that gives the orthogonal fragment densities.
TYPE:
INTEGER
DEFAULT:
6
OPTIONS:
$n$ $10^{-n}$
RECOMMENDATION:
Use the default unless tighter convergence is preferred.

FRZ_ORTHO_DECOMP
Perform the decomposition of frozen interaction energy based on the orthogonal decomposition of the 1PDM associated with the frozen wave function.
TYPE:
BOOLEAN
DEFAULT:
FALSE (automatically set to TRUE by EDA2 options 1–5)
OPTIONS:
FALSE Do not perform the orthogonal decomposition. TRUE Perform the frozen energy decomposition using orthogonal fragment densities.
RECOMMENDATION:
Use default value automatically set by “EDA2". Note that users are allowed to turn off the orthogonal decomposition by setting FRZ_ORTHO_DECOMP to -1. Also, for calculations that involve ECPs, it is automatically set to FALSE since unreasonable results will be produced otherwise.

FSM_MODE
Specifies the method of interpolation
TYPE:
INTEGER
DEFAULT:
2
OPTIONS:
1 Cartesian 2 LST
RECOMMENDATION:
In most cases, LST is superior to Cartesian interpolation.

Specifies the number of perpendicular gradient steps used to optimize each node
TYPE:
INTEGER
DEFAULT:
Undefined
OPTIONS:
$N$ Number of perpendicular gradients per node
RECOMMENDATION:
Anything between 2 and 6 should work, where increasing the number is only needed for difficult reaction paths.

FSM_NNODE
Specifies the number of nodes along the string
TYPE:
INTEGER
DEFAULT:
Undefined
OPTIONS:
$N$ number of nodes in FSM calculation
RECOMMENDATION:
$N=15$. Use 10 to 20 nodes for a typical calculation. Reaction paths that connect multiple elementary steps should be separated into individual elementary steps, and one FSM job run for each pair of intermediates. Use a higher number when the FSM is followed by an approximate-Hessian based transition state search (Section 10.2.2).

FSM_OPT_MODE
Specifies the method of optimization
TYPE:
INTEGER
DEFAULT:
Undefined
OPTIONS:
1 Conjugate gradients 2 Quasi-Newton method with BFGS Hessian update
RECOMMENDATION:
The quasi-Newton method is more efficient when the number of nodes is high.

FSSH_CONTINUE
Restart a FSSH calculation from a previous run, using the file 396.0. When this is enabled, the initial conditions of the surface hopping calculation will be set, including the correct wave function amplitudes, initial surface, and position/momentum moments (if AFSSH) from the final step of some prior calculation.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$0$ Start fresh calculation. $1$ Restart from previous run.
RECOMMENDATION:
None

FSSH_INITIALSURFACE
Specifies the initial state in a surface hopping calculation.
TYPE:
INTEGER
DEFAULT:
None
OPTIONS:
$n$ An integer between FSSH_LOWESTSURFACE and FSSH_LOWESTSURFACE $+$ FSSH_NSURFACES $-1$.
RECOMMENDATION:
None

FSSH_LOWESTSURFACE
Specifies the lowest-energy state considered in a surface hopping calculation.
TYPE:
INTEGER
DEFAULT:
None
OPTIONS:
$n$ Only states $n$ and above are considered in a FSSH calculation.
RECOMMENDATION:
None

FSSH_NSURFACES
Specifies the number of states considered in a surface hopping calculation.
TYPE:
INTEGER
DEFAULT:
None
OPTIONS:
$n$ $n$ states are considered in the surface hopping calculation.
RECOMMENDATION:
Any states which may come close in energy to the active surface should be included in the surface hopping calculation.

FTC_CLASS_THRESH_MULT
Together with FTC_CLASS_THRESH_ORDER, determines the cutoff threshold for included a shell-pair in the $dd$ class, i.e., the class that is expanded in terms of plane waves.
TYPE:
INTEGER
DEFAULT:
5 Multiplicative part of the FTC classification threshold. Together with the default value of the FTC_CLASS_THRESH_ORDER this leads to the $5\times 10^{-5}$ threshold value.
OPTIONS:
$n$ User specified.
RECOMMENDATION:
Use the default. If diffuse basis sets are used and the molecule is relatively big then tighter FTC classification threshold has to be used. According to our experiments using Pople-type diffuse basis sets, the default $5\times 10^{-5}$ value provides accurate result for an alanine5 molecule while $1\times 10^{-5}$ threshold value for alanine10 and $5\times 10^{-6}$ value for alanine15 has to be used.

FTC_CLASS_THRESH_ORDER
Together with FTC_CLASS_THRESH_MULT, determines the cutoff threshold for included a shell-pair in the $dd$ class, i.e., the class that is expanded in terms of plane waves.
TYPE:
INTEGER
DEFAULT:
5 Logarithmic part of the FTC classification threshold. Corresponds to $10^{-5}$
OPTIONS:
$n$ User specified
RECOMMENDATION:
Use the default.

FTC_SMALLMOL
Controls whether or not the operator is evaluated on a large grid and stored in memory to speed up the calculation.
TYPE:
INTEGER
DEFAULT:
1
OPTIONS:
1 Use a big pre-calculated array to speed up the FTC calculations 0 Use this option to save some memory
RECOMMENDATION:
Use the default if possible and use 0 (or buy some more memory) when needed.

FTC
Controls the overall use of the FTC.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 Do not use FTC in the Coulomb part 1 Use FTC in the Coulomb part
RECOMMENDATION:
Use FTC when bigger and/or diffuse basis sets are used.

GAUSSIAN_BLUR
Enables the use of Gaussian-delocalized external charges in a QM/MM calculation.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE Delocalizes external charges with Gaussian functions. FALSE Point charges
RECOMMENDATION:
None

GAUSS_BLUR_WIDTH
Delocalization width for external MM Gaussian charges in a Janus calculations.
TYPE:
INTEGER
DEFAULT:
NONE
OPTIONS:
$n$ Use a width of $n\times 10^{-4}$ Å.
RECOMMENDATION:
Blur all MM external charges in a QM/MM calculation with the specified width. Gaussian blurring is currently incompatible with PCM calculations. Values of 1.0–2.0 Å are recommended in Ref. 208.

GEN_SCFMAN_ALGO_1
The first algorithm to be used in a hybrid-algorithm calculation.
TYPE:
STRING
DEFAULT:
0
OPTIONS:
All the available SCF_ALGORITHM options, including the GEN_SCFMAN additions (Section 4.3.1).
RECOMMENDATION:
None

GEN_SCFMAN_CONV_1
The convergence criterion given to the first algorithm. If reached, switch to the next algorithm.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$n$ 10${}^{-n}$
RECOMMENDATION:
None

GEN_SCFMAN_HYBRID_ALGO
Use multiple algorithms in an SCF calculation based on GEN_SCFMAN.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
FALSE Use a single SCF algorithm (given by SCF_ALGORITHM). TRUE Use multiple SCF algorithms (to be specified).
RECOMMENDATION:
Set it to TRUE when the use of more than one algorithm is desired.

GEN_SCFMAN_ITER_1
Maximum number of iterations given to the first algorithm. If used up, switch to the next algorithm.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
User-defined
RECOMMENDATION:
None

GEN_SCFMAN
Use GEN_SCFMAN for the present SCF calculation.
TYPE:
BOOLEAN
DEFAULT:
TRUE
OPTIONS:
FALSE Use the previous SCF code. TRUE Use GEN_SCFMAN.
RECOMMENDATION:
Set to FALSE in cases where features not yet supported by GEN_SCFMAN are needed.

GEOM_OPT_CHARAC_CONV
Overide the built-in convergence criterion for the Davidson solver.
TYPE:
INTEGER
DEFAULT:
0 (use the built-in default value 10${}^{-5}$)
OPTIONS:
$n$ Set the convergence criterion to 10${}^{-n}$.
RECOMMENDATION:
Use the default. If it fails to converge, consider loosening the criterion with caution.

GEOM_OPT_CHARAC
Use the finite difference Davidson method to characterize the resulting energy minimum/transition state.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
FALSE do not characterize the resulting stationary point. TRUE perform a characterization of the stationary point.
RECOMMENDATION:
Set it to TRUE when the character of a stationary point needs to be verified, especially for a transition structure.

GEOM_OPT_COORDS
Controls the type of optimization coordinates.
TYPE:
INTEGER
DEFAULT:
$-$1
OPTIONS:
0 Optimize in Cartesian coordinates.  1 Generate and optimize in internal coordinates, if this fails abort. $-$1 Generate and optimize in internal coordinates, if this fails at any stage of the optimization, switch to Cartesian and continue.  2 Optimize in $Z$-matrix coordinates, if this fails abort. $-$2 Optimize in $Z$-matrix coordinates, if this fails during any stage of the optimization switch to Cartesians and continue.
RECOMMENDATION:
Use the default, as delocalized internals are more efficient. Note that optimization in $Z$-matrix coordinates requires that the input be specified in $Z$-matrix format.

GEOM_OPT_DMAX
Maximum allowed step size. Value supplied is multiplied by 10${}^{-3}$.
TYPE:
INTEGER
DEFAULT:
300 = 0.3
OPTIONS:
$n$ User-defined cutoff.
RECOMMENDATION:
Use the default.

GEOM_OPT_HESSIAN
Determines the initial Hessian status.
TYPE:
STRING
DEFAULT:
DIAGONAL
OPTIONS:
DIAGONAL Set up diagonal Hessian. READ Have exact or initial Hessian. Use as is if Cartesian, or transform if internals.
RECOMMENDATION:
An accurate initial Hessian will improve the performance of the optimizer, but is expensive to compute.

GEOM_OPT_LINEAR_ANGLE
Threshold for near linear bond angles (degrees).
TYPE:
INTEGER
DEFAULT:
165 degrees.
OPTIONS:
$n$ User-defined level.
RECOMMENDATION:
Use the default.

GEOM_OPT_MAX_CYCLES
Maximum number of optimization cycles.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
$n$ User defined positive integer.
RECOMMENDATION:
The default should be sufficient for most cases. Increase if the initial guess geometry is poor, or for systems with shallow potential wells.

GEOM_OPT_MAX_DIIS
Controls maximum size of subspace for GDIIS.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 Do not use GDIIS. -1 Default size = min(NDEG, NATOMS, 4) NDEG = number of molecular degrees of freedom. $n$ Size specified by user.
RECOMMENDATION:
Use the default or do not set $n$ too large.

GEOM_OPT_MODE
Determines Hessian mode followed during a transition state search.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 Mode following off. $n$ Maximize along mode $n$.
RECOMMENDATION:
Use the default, for geometry optimizations.

GEOM_OPT_PRINT
Controls the amount of Optimize print output.
TYPE:
INTEGER
DEFAULT:
3 Error messages, summary, warning, standard information and gradient print out.
OPTIONS:
0 Error messages only. 1 Level 0 plus summary and warning print out. 2 Level 1 plus standard information. 3 Level 2 plus gradient print out. 4 Level 3 plus Hessian print out. 5 Level 4 plus iterative print out. 6 Level 5 plus internal generation print out. 7 Debug print out.
RECOMMENDATION:
Use the default.

GEOM_OPT_SYMFLAG
Controls the use of symmetry in Optimize.
TYPE:
LOGICAL
DEFAULT:
TRUE
OPTIONS:
TRUE Make use of point group symmetry. FALSE Do not make use of point group symmetry.
RECOMMENDATION:
Use the default.

GEOM_OPT_TOL_DISPLACEMENT
Convergence on maximum atomic displacement.
TYPE:
INTEGER
DEFAULT:
1200 $\equiv 1200\times 10^{-6}$ tolerance on maximum atomic displacement.
OPTIONS:
$n$ Integer value (tolerance = $n\times 10^{-6}$).
RECOMMENDATION:
Use the default. To converge GEOM_OPT_TOL_GRADIENT and one of GEOM_OPT_TOL_DISPLACEMENT and GEOM_OPT_TOL_ENERGY must be satisfied.

GEOM_OPT_TOL_ENERGY
Convergence on energy change of successive optimization cycles.
TYPE:
INTEGER
DEFAULT:
100 $\equiv 100\times 10^{-8}$ tolerance on maximum (absolute) energy change.
OPTIONS:
$n$ Integer value (tolerance = value $n\times 10^{-8}$).
RECOMMENDATION:
Use the default. To converge GEOM_OPT_TOL_GRADIENT and one of GEOM_OPT_TOL_DISPLACEMENT and GEOM_OPT_TOL_ENERGY must be satisfied.

TYPE:
INTEGER
DEFAULT:
300 $\equiv 300\times 10^{-6}$ tolerance on maximum gradient component.
OPTIONS:
$n$ Integer value (tolerance = $n\times 10^{-6}$).
RECOMMENDATION:
Use the default. To converge GEOM_OPT_TOL_GRADIENT and one of GEOM_OPT_TOL_DISPLACEMENT and GEOM_OPT_TOL_ENERGY must be satisfied.

GEOM_OPT_UPDATE
Controls the Hessian update algorithm.
TYPE:
INTEGER
DEFAULT:
-1
OPTIONS:
-1 Use the default update algorithm.  0 Do not update the Hessian (not recommended).  1 Murtagh-Sargent update.  2 Powell update.  3 Powell/Murtagh-Sargent update (TS default).  4 BFGS update (OPT default).  5 BFGS with safeguards to ensure retention of positive definiteness (GDISS default).
RECOMMENDATION:
Use the default.

GEOM_PRINT
Controls the amount of geometric information printed at each step.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE Prints out all geometric information; bond distances, angles, torsions. FALSE Normal printing of distance matrix.
RECOMMENDATION:
Use if you want to be able to quickly examine geometric parameters at the beginning and end of optimizations. Only prints in the beginning of single point energy calculations.

GHF
Run a generalized Hartree-Fock calculation with GEN_SCFMAN.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
TRUE Run a GHF calculation. FALSE Do not use GHF.
RECOMMENDATION:
Set to TRUE if desired.

GRAIN
Controls the number of lowest-level boxes in one dimension for CFMM.
TYPE:
INTEGER
DEFAULT:
-1 Program decides best value, turning on CFMM when useful
OPTIONS:
-1 Program decides best value, turning on CFMM when useful 1 Do not use CFMM $n\geq 8$ Use CFMM with $n$ lowest-level boxes in one dimension
RECOMMENDATION:
This is an expert option; either use the default, or use a value of 1 if CFMM is not desired.

GVB_AMP_SCALE
Scales the default orbital amplitude iteration step size by $n$/1000 for IP/RCC. PP amplitude equations are solved analytically, so this parameter does not affect PP.
TYPE:
INTEGER
DEFAULT:
1000 Corresponding to 100%
OPTIONS:
$n$ User-defined, 0–1000
RECOMMENDATION:
Default is usually fine, but in some highly-correlated systems it can help with convergence to use smaller values.

GVB_DO_ROHF
Sets the number of Unrestricted-in-Active Pairs to be kept restricted.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$n$ User-Defined
RECOMMENDATION:
If $n$ is the same value as GVB_N_PAIRS returns the ROHF solution for GVB, only works with the UNRESTRICTED = TRUE implementation of GVB with GVB_OLD_UPP = 0 (its default value)

GVB_DO_SANO
Sets the scheme used in determining the active virtual orbitals in a Unrestricted-in-Active Pairs GVB calculation.
TYPE:
INTEGER
DEFAULT:
2
OPTIONS:
0 No localization or Sano procedure 1 Only localizes the active virtual orbitals 2 Uses the Sano procedure
RECOMMENDATION:
Different initial guesses can sometimes lead to different solutions. Disabling sometimes can aid in finding more non-local solutions for the orbitals.

GVB_GUESS_MIX
Similar to SCF_GUESS_MIX, it breaks alpha/beta symmetry for UPP by mixing the alpha HOMO and LUMO orbitals according to the user-defined fraction of LUMO to add the HOMO. 100 corresponds to a 1:1 ratio of HOMO and LUMO in the mixed orbitals.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$n$ User-defined, $0\leq n\leq 100$
RECOMMENDATION:
25 often works well to break symmetry without overly impeding convergence.

GVB_LOCAL
Sets the localization scheme used in the initial guess wave function.
TYPE:
INTEGER
DEFAULT:
2 Pipek-Mezey orbitals
OPTIONS:
0 No Localization 1 Boys localized orbitals 2 Pipek-Mezey orbitals
RECOMMENDATION:
Different initial guesses can sometimes lead to different solutions. It can be helpful to try both to ensure the global minimum has been found.

GVB_N_PAIRS
Alternative to CC_REST_OCC and CC_REST_VIR for setting active space size in GVB and valence coupled cluster methods.
TYPE:
INTEGER
DEFAULT:
PP active space (1 occ and 1 virt for each valence electron pair)
OPTIONS:
$n$ user-defined
RECOMMENDATION:
Use the default unless one wants to study a special active space. When using small active spaces, it is important to ensure that the proper orbitals are incorporated in the active space. If not, use the $reorder_mo feature to adjust the SCF orbitals appropriately. GVB_OLD_UPP Which unrestricted algorithm to use for GVB. TYPE: INTEGER DEFAULT: 0 OPTIONS: 0 Use Unrestricted-in-Active Pairs described in Ref. 535 1 Use Unrestricted Implementation described in Ref. 79 RECOMMENDATION: Only works for Unrestricted PP and no other GVB model. GVB_ORB_CONV The GVB-CC wave function is considered converged when the root-mean-square orbital gradient and orbital step sizes are less than $10^{-\mathrm{GVB\_ORB\_CONV}}$. Adjust THRESH simultaneously. TYPE: INTEGER DEFAULT: 5 OPTIONS: $n$ User-defined RECOMMENDATION: Use 6 for PP(2) jobs or geometry optimizations. Tighter convergence (i.e. 7 or higher) cannot always be reliably achieved. GVB_ORB_MAX_ITER Controls the number of orbital iterations allowed in GVB-CC calculations. Some jobs, particularly unrestricted PP jobs can require 500–1000 iterations. TYPE: INTEGER DEFAULT: 256 OPTIONS: User-defined number of iterations. RECOMMENDATION: Default is typically adequate, but some jobs, particularly UPP jobs, can require 500–1000 iterations if converged tightly. GVB_ORB_SCALE Scales the default orbital step size by $n$/1000. TYPE: INTEGER DEFAULT: 1000 Corresponding to 100% OPTIONS: $n$ User-defined, 0–1000 RECOMMENDATION: Default is usually fine, but for some stretched geometries it can help with convergence to use smaller values. GVB_POWER Coefficient for GVB_IP exchange type amplitude regularization to improve the convergence of the amplitude equations especially for spin-unrestricted amplitudes near dissociation. This is the leading coefficient for an amplitude dampening term included in the energy denominator: -($c$/10000)$(e^{t_{ij}^{p}}-1)/(e^{1}-1)$ TYPE: INTEGER DEFAULT: 6 OPTIONS: $p$ User-defined RECOMMENDATION: Should be decreased if unrestricted amplitudes do not converge or converge slowly at dissociation, and should be kept even valued. GVB_PRINT Controls the amount of information printed during a GVB-CC job. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined RECOMMENDATION: Should never need to go above 0 or 1. GVB_REGULARIZE Coefficient for GVB_IP exchange type amplitude regularization to improve the convergence of the amplitude equations especially for spin-unrestricted amplitudes near dissociation. This is the leading coefficient for an amplitude dampening term ${-(c/10000)(e^{t_{ij}^{p}}-1)/(e^{1}-1)}$ TYPE: INTEGER DEFAULT: 0 For restricted 1 For unrestricted OPTIONS: $c$ User-defined RECOMMENDATION: Should be increased if unrestricted amplitudes do not converge or converge slowly at dissociation. Set this to zero to remove all dynamically-valued amplitude regularization. GVB_REORDER_1 Tells the code which two pairs to swap first. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined XXXYYY RECOMMENDATION: This is in the format of two 3-digit pair indices that tell the code to swap pair XXX with YYY, for example swapping pair 1 and 2 would get the input 001002. Must be specified in GVB_REORDER_PAIRS $\geq$ 1. GVB_REORDER_2 Tells the code which two pairs to swap second. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined XXXYYY RECOMMENDATION: This is in the format of two 3-digit pair indices that tell the code to swap pair XXX with YYY, for example swapping pair 1 and 2 would get the input 001002. Must be specified in GVB_REORDER_PAIRS $\geq$ 2. GVB_REORDER_3 Tells the code which two pairs to swap third. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined XXXYYY RECOMMENDATION: This is in the format of two 3-digit pair indices that tell the code to swap pair XXX with YYY, for example swapping pair 1 and 2 would get the input 001002. Must be specified in GVB_REORDER_PAIRS $\geq$ 3. GVB_REORDER_4 Tells the code which two pairs to swap fourth. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined XXXYYY RECOMMENDATION: This is in the format of two 3-digit pair indices that tell the code to swap pair XXX with YYY, for example swapping pair 1 and 2 would get the input 001002. Must be specified in GVB_REORDER_PAIRS $\geq$ 4. GVB_REORDER_5 Tells the code which two pairs to swap fifth. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined XXXYYY RECOMMENDATION: This is in the format of two 3-digit pair indices that tell the code to swap pair XXX with YYY, for example swapping pair 1 and 2 would get the input 001002. Must be specified in GVB_REORDER_PAIRS $\geq$ 5. GVB_REORDER_PAIRS Tells the code how many GVB pairs to switch around. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ $0\leq n\leq 5$ RECOMMENDATION: This allows for the user to change the order the active pairs are placed in after the orbitals are read in or are guessed using localization and the Sano procedure. Up to 5 sequential pair swaps can be made, but it is best to leave this alone. GVB_RESTART Restart a job from previously-converged GVB-CC orbitals. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE/FALSE RECOMMENDATION: Useful when trying to converge to the same GVB solution at slightly different geometries, for example. GVB_SHIFT Value for a statically valued energy shift in the energy denominator used to solve the coupled cluster amplitude equations, $n$/10000. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined RECOMMENDATION: Default is fine, can be used in lieu of the dynamically valued amplitude regularization if it does not aid convergence. GVB_SYMFIX Should GVB use a symmetry breaking fix. TYPE: INTEGER DEFAULT: 0 OPTIONS: 0 no symmetry breaking fix 1 symmetry breaking fix with virtual orbitals spanning the active space 2 symmetry breaking fix with virtual orbitals spanning the whole virtual space RECOMMENDATION: It is best to stick with type 1 to get a symmetry breaking correction with the best results coming from CORRELATION=NP and GVB_SYMFIX = 1. GVB_SYMPEN Sets the pre-factor for the amplitude regularization term for the SB amplitudes. TYPE: INTEGER DEFAULT: 160 OPTIONS: $\gamma$ User-defined RECOMMENDATION: Sets the pre-factor for the amplitude regularization term for the SB amplitudes: $-(\gamma/1000)(e^{(c*100)*t^{2}}-1)$. GVB_SYMSCA Sets the weight for the amplitude regularization term for the SB amplitudes. TYPE: INTEGER DEFAULT: 125 OPTIONS: $c$ User-defined RECOMMENDATION: Sets the weight for the amplitude regularization term for the SB amplitudes: $-(\gamma/1000)(e^{(c*100)*t^{2}}-1)$. GVB_TRUNC_OCC Controls how many pairs’ occupied orbitals are truncated from the GVB active space. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined RECOMMENDATION: This allows for asymmetric GVB active spaces removing the $n$ lowest energy occupied orbitals from the GVB active space while leaving their paired virtual orbitals in the active space. Only the models including the SIP and DIP amplitudes (ie NP and 2P) benefit from this all other models this equivalent to just reducing the total number of pairs. GVB_TRUNC_VIR Controls how many pairs’ virtual orbitals are truncated from the GVB active space. TYPE: INTEGER DEFAULT: 0 OPTIONS: $n$ User-defined RECOMMENDATION: This allows for asymmetric GVB active spaces removing the $n$ highest energy occupied orbitals from the GVB active space while leaving their paired virtual orbitals in the active space. Only the models including the SIP and DIP amplitudes (ie NP and 2P) benefit from this all other models this equivalent to just reducing the total number of pairs. GVB_UNRESTRICTED Controls restricted versus unrestricted PP jobs. Usually handled automatically. TYPE: LOGICAL DEFAULT: same value as UNRESTRICTED OPTIONS: TRUE/FALSE RECOMMENDATION: Set this variable explicitly only to do a UPP job from an RHF or ROHF initial guess. Leave this variable alone and specify UNRESTRICTED = TRUE to access the new Unrestricted-in-Active-Pairs GVB code which can return an RHF or ROHF solution if used with GVB_DO_ROHF HESS_AND_GRAD Enables the evaluation of both analytical gradient and Hessian in a single job TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Evaluates both gradient and Hessian. FALSE Evaluates Hessian only. RECOMMENDATION: Use only in a frequency (and thus Hessian) evaluation. HFPT_BASIS Specifies the secondary basis in a HFPC/DFPC calculation. TYPE: STRING DEFAULT: None OPTIONS: None RECOMMENDATION: See reference for recommended basis set, functional, and grid pairings. HFPT Activates HFPC/DFPC calculation. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: Single-point energy only RECOMMENDATION: Use Dual-Basis to capture large-basis effects at smaller basis cost. See reference for recommended basis set, functional, and grid pairings. HF_LR Sets the fraction of Hartree-Fock exchange at $r_{12}=\infty$. TYPE: INTEGER DEFAULT: No default OPTIONS: $n$ Corresponding to HF_LR = $n/1000$ RECOMMENDATION: None HF_SR Sets the fraction of Hartree-Fock exchange at $r_{12}=0$. TYPE: INTEGER DEFAULT: No default OPTIONS: $n$ Corresponding to HF_SR = $n/1000$ RECOMMENDATION: None HIRSHFELD_CONV Set different SCF convergence criterion for the calculation of the single-atom Hirshfeld calculations TYPE: INTEGER DEFAULT: same as SCF_CONVERGENCE OPTIONS: $n$ Corresponding to $10^{-n}$ RECOMMENDATION: 5 HIRSHFELD_READ Switch to force reading in of isolated atomic densities. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Read in isolated atomic densities from previous Hirshfeld calculation from disk. FALSE Generate new isolated atomic densities. RECOMMENDATION: Use the default unless system is large. Note, atoms should be in the same order with same basis set used as in the previous Hirshfeld calculation (although coordinates can change). The previous calculation should be run with the -save switch. HIRSHFELD_SPHAVG Controls whether atomic densities should be spherically averaged in pro-molecule. TYPE: LOGICAL DEFAULT: TRUE OPTIONS: TRUE Spherically average atomic densities. FALSE Do not spherically average. RECOMMENDATION: Use the default. HIRSHFELD Controls running of Hirshfeld population analysis. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Calculate Hirshfeld populations. FALSE Do not calculate Hirshfeld populations. RECOMMENDATION: None HIRSHITER_THRESH Controls the convergence criterion of iterative Hirshfeld population analysis. TYPE: INTEGER DEFAULT: 5 OPTIONS: $N$ Corresponding to the convergence criterion of $N/10000$, in $e$. RECOMMENDATION: Use the default, which is the value recommended in Ref. 123 HIRSHITER Controls running of iterative Hirshfeld population analysis. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Calculate iterative Hirshfeld populations. FALSE Do not calculate iterative Hirshfeld populations. RECOMMENDATION: None HIRSHMOD Apply modifiers to the free-atom volumes used in the calculation of the scaled TS-vdW parameters TYPE: INTEGER DEFAULT: 4 OPTIONS: 0 Do not apply modifiers to the Hirshfeld volumes. 1 Apply built-in modifier to H. 2 Apply built-in modifier to H and C. 3 Apply built-in modifier to H, C and N. 4 Apply built-in modifier to H, C, N and O RECOMMENDATION: Use the default IDERIV Controls the order of derivatives that are evaluated analytically. The user is not normally required to specify a value, unless numerical derivatives are desired. The derivatives will be evaluated numerically if IDERIV is set lower than JOBTYPE requires. TYPE: INTEGER DEFAULT: Set to the order of derivative that JOBTYPE requires OPTIONS: 2 Analytic second derivatives of the energy (Hessian) 1 Analytic first derivatives of the energy. 0 Analytic energies only. RECOMMENDATION: Usually set to the maximum possible for efficiency. Note that IDERIV will be set lower if analytic derivatives of the requested order are not available. IGNORE_LOW_FREQ Low frequencies that should be treated as rotation can be ignored during anharmonic correction calculation. TYPE: INTEGER DEFAULT: 300 Corresponding to 300 cm${}^{-1}$. OPTIONS: $n$ Any mode with harmonic frequency less than $n$ will be ignored. RECOMMENDATION: Use the default. INCDFT_DENDIFF_THRESH Sets the threshold for screening density matrix values in the IncDFT procedure. TYPE: INTEGER DEFAULT: SCF_CONVERGENCE + 3 OPTIONS: $n$ Corresponding to a threshold of $10^{-n}$. RECOMMENDATION: If the default value causes convergence problems, set this value higher to tighten the threshold. INCDFT_DENDIFF_VARTHRESH Sets the lower bound for the variable threshold for screening density matrix values in the IncDFT procedure. The threshold will begin at this value and then vary depending on the error in the current SCF iteration until the value specified by INCDFT_DENDIFF_THRESH is reached. This means this value must be set lower than INCDFT_DENDIFF_THRESH. TYPE: INTEGER DEFAULT: 0 Variable threshold is not used. OPTIONS: $n$ Corresponding to a threshold of $10^{-n}$. RECOMMENDATION: If the default value causes convergence problems, set this value higher to tighten accuracy. If this fails, set to 0 and use a static threshold. INCDFT_GRIDDIFF_THRESH Sets the threshold for screening functional values in the IncDFT procedure TYPE: INTEGER DEFAULT: SCF_CONVERGENCE + 3 OPTIONS: $n$ Corresponding to a threshold of $10^{-n}$. RECOMMENDATION: If the default value causes convergence problems, set this value higher to tighten the threshold. INCDFT_GRIDDIFF_VARTHRESH Sets the lower bound for the variable threshold for screening the functional values in the IncDFT procedure. The threshold will begin at this value and then vary depending on the error in the current SCF iteration until the value specified by INCDFT_GRIDDIFF_THRESH is reached. This means that this value must be set lower than INCDFT_GRIDDIFF_THRESH. TYPE: INTEGER DEFAULT: 0 Variable threshold is not used. OPTIONS: $n$ Corresponding to a threshold of $10^{-n}$. RECOMMENDATION: If the default value causes convergence problems, set this value higher to tighten accuracy. If this fails, set to 0 and use a static threshold. INCDFT Toggles the use of the IncDFT procedure for DFT energy calculations. TYPE: LOGICAL DEFAULT: TRUE OPTIONS: FALSE Do not use IncDFT TRUE Use IncDFT RECOMMENDATION: Turning this option on can lead to faster SCF calculations, particularly towards the end of the SCF. Please note that for some systems use of this option may lead to convergence problems. INCFOCK Iteration number after which the incremental Fock matrix algorithm is initiated TYPE: INTEGER DEFAULT: 1 Start INCFOCK after iteration number 1 OPTIONS: User-defined (0 switches INCFOCK off) RECOMMENDATION: May be necessary to allow several iterations before switching on INCFOCK. INTEGRALS_BUFFER Controls the size of in-core integral storage buffer. TYPE: INTEGER DEFAULT: 15 15 Megabytes. OPTIONS: User defined size. RECOMMENDATION: Use the default, or consult your systems administrator for hardware limits. INTEGRAL_2E_OPR Determines the two-electron operator. TYPE: INTEGER DEFAULT: -2 Coulomb Operator. OPTIONS: -1 Apply the CASE approximation. -2 Coulomb Operator. RECOMMENDATION: Use the default unless the CASE operator is desired. INTERNAL_STABILITY_CONV Convergence criterion for the Davidson solver (for the lowest eigenvalues). TYPE: INTEGER DEFAULT: 4 (3 when FD_MAT_ON_VECS = TRUE) OPTIONS: $n$ Terminate Davidson iterations when the norm of the residual vector is below 10${}^{-n}$. RECOMMENDATION: Use the default. INTERNAL_STABILITY_DAVIDSON_ITER Maximum number of Davidson iterations allowed in one stability analysis. TYPE: INTEGER DEFAULT: 50 OPTIONS: $n$ Perform up to $n$ Davidson iterations. RECOMMENDATION: Use the default. INTERNAL_STABILITY_ITER Maximum number of new SCF calculations permitted after the first stability analysis is performed. TYPE: INTEGER DEFAULT: 0 (automatically set to 1 if INTERNAL_STABILITY = TRUE) OPTIONS: $n$ $n$ new SCF calculations permitted. RECOMMENDATION: Give a larger number if 1 is not enough (still unstable). INTERNAL_STABILITY_ROOTS Number of lowest Hessian eigenvalues to solve for. TYPE: INTEGER DEFAULT: 2 OPTIONS: $n$ Solve for $n$ lowest eigenvalues. RECOMMENDATION: Use the default. INTERNAL_STABILITY Perform internal stability analysis in GEN_SCFMAN. TYPE: BOOLEAN DEFAULT: FALSE OPTIONS: FALSE Do not perform internal stability analysis after convergence. TRUE Perform internal stability analysis and generate the corrected MOs. RECOMMENDATION: Turn it on when the SCF solution is prone to unstable solutions, especially for open-shell species. INTRACULE Controls whether intracule properties are calculated (see also the$intracule section).
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE No intracule properties. TRUE Evaluate intracule properties.
RECOMMENDATION:
None

IP_STATES
Sets the number of ionized target states roots to find. By default, $\beta$ electron will be removed (see EOM_IP_BETA).
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0 Do not look for any IP states.
OPTIONS:
$[i,j,k\ldots]$ Find $i$ ionized states in the first irrep, $j$ states in the second irrep etc.
RECOMMENDATION:
None

IQMOL_FCHK
Controls printing of a formatted checkpoint file that can be read by the IQmol program.
TYPE:
LOGICAL
DEFAULT:
FALSE Do not generate the checkpoint file.
OPTIONS:
TRUE Generate a checkpoint file named inputfilename.fchk.
RECOMMENDATION:
For many Q-Chem jobs there is no reason not to generate the checkpoint file. Note that GUI = 2 (used by IQmol) is synonymous with IQMOL_FCHK = TRUE.

ISOTOPES
Specifies if non-default masses are to be used in the frequency calculation.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE Use default masses only. TRUE Read isotope masses from $isotopes section. RECOMMENDATION: None 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. RPATH Intrinsic reaction path following. RECOMMENDATION: Application-dependent. KS_GAP_PRINT Control printing of (generalized Kohn-Sham) HOMO-LUMO gap information. TYPE: Boolean DEFAULT: false OPTIONS: false (default) do not print gap information true print gap information RECOMMENDATION: Use in conjunction with KS_GAP_UNIT if true. KS_GAP_UNIT Unit for KS_GAP_PRINT and FOA_FUNDGAP (see Section 5.11) TYPE: INTEGER DEFAULT: 0 OPTIONS: 0 (default) hartrees 1 eV RECOMMENDATION: none LB94_BETA Sets the $\beta$ parameter for the LB94 XC potential TYPE: INTEGER DEFAULT: 500 OPTIONS: $n$ Corresponding to $\beta=n/10000$. RECOMMENDATION: Use the default. LIBPT_MIXED_PRECISION Deploys single-precision evaluation of (T) and (fT) within libpt TYPE: INTEGER DEFAULT: 0 do not use single precision OPTIONS: 1 use single precision RECOMMENDATION: Use in combination with USE_LIBPT. LINK_ATOM_PROJECTION Controls whether to perform a link-atom projection TYPE: LOGICAL DEFAULT: TRUE OPTIONS: TRUE Performs the projection FALSE No projection RECOMMENDATION: Necessary in a full QM/MM Hessian evaluation on a system with link atoms LIN_K Controls whether linear scaling evaluation of exact exchange (LinK) is used. TYPE: LOGICAL DEFAULT: Program chooses, switching on LinK whenever CFMM is used. OPTIONS: TRUE Use LinK FALSE Do not use LinK RECOMMENDATION: Use for HF and hybrid DFT calculations with large numbers of atoms. LOBA_THRESH Specifies the thresholds to use for LOBA TYPE: INTEGER DEFAULT: 6015 OPTIONS: $aabb$ $aa$ specifies the threshold to use for localization $bb$ specifies the threshold to use for occupation Both are given as percentages. RECOMMENDATION: Decrease $bb$ to see the smaller contributions to orbitals. Values of $aa$ between 40 and 75 have been shown to given meaningful results. LOBA Specifies the methods to use for LOBA TYPE: INTEGER DEFAULT: 00 OPTIONS: $ab$ $a$ specifies the localization method 0 Perform Boys localization. 1 Perform PM localization. 2 Perform ER localization. $b$ specifies the population analysis method 0 Do not perform LOBA. This is the default. 1 Use Mulliken population analysis. 2 Use Löwdin population analysis. RECOMMENDATION: Boys Localization is the fastest. ER will require an auxiliary basis set. LOBA 12 provides a reasonable speed/accuracy compromise. LOCALFREQ_GROUP1 Select the number of modes to include in the first subset of modes to localize independently when the keyword LOCALFREQ_GROUPS > 0. TYPE: INTEGER DEFAULT: NONE OPTIONS: $n$ User-specified integer. RECOMMENDATION: Modes will be included starting with the lowest frequency mode and then in ascending energy order up to the defined value. LOCALFREQ_GROUPS Select the number of groups of frequencies to be localized separately within a localized mode calculation. The size of the groups are then controlled using the LOCALFREQ_GROUP1, LOCALFREQ_GROUP2, and LOCALFREQ_GROUP3 keywords. TYPE: INTEGER DEFAULT: 0 Localize all normal modes together. OPTIONS: 1 Define one subset of modes to localize independently. 2 Define two subsets of modes to localize independently. 3 Define three subsets of modes to localize independently. RECOMMENDATION: None LOCALFREQ_MAX_ITER Controls the maximum number of mode localization sweeps permitted. TYPE: INTEGER DEFAULT: 200 OPTIONS: $n$ User-specified integer. RECOMMENDATION: None LOCALFREQ_SELECT Select a subset of normal modes for subsequent anharmonic frequency analysis. TYPE: LOGICAL DEFAULT: FALSE Use all normal modes. OPTIONS: TRUE Select a subset of normal modes. RECOMMENDATION: None LOCALFREQ_THRESH Mode localization is considered converged when the change in the localization criterion is less than $10^{\mathrm{-LOCALFREQ\_THRESH}}$. TYPE: INTEGER DEFAULT: 6 OPTIONS: $n$ User-specified integer. RECOMMENDATION: None LOCALFREQ Controls whether a vibrational mode localization calculation is performed. TYPE: INTEGER DEFAULT: 0 Normal mode calculation. OPTIONS: 1 Localized mode calculation with a Pipek-Mezey like criterion. 2 Localized mode calculation with a Boys like criterion. RECOMMENDATION: None LOCAL_INTERP_ORDER Controls the order of the B-spline TYPE: INTEGER DEFAULT: 6 OPTIONS: $n$ An integer RECOMMENDATION: The default value is sufficiently accurate LOC_CIS_OV_SEPARATE Decide whether or not to localized the “occupied” and “virtual” components of the localized diabatization function, i.e., whether to localize the electron attachments and detachments separately. TYPE: LOGICAL DEFAULT: FALSE Do not separately localize electron attachments and detachments. OPTIONS: TRUE RECOMMENDATION: If one wants to use Boys localized diabatization for energy transfer (as opposed to electron transfer) , this is a necessary option. ER is more rigorous technique, and does not require this OV feature, but will be somewhat slower. LOWDIN_POPULATION Run Löwdin population analysis. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: FALSE Do not calculate Löwdin populations. TRUE Run Löwdin population analysis. RECOMMENDATION: None LRC_DFT Controls the application of long-range-corrected DFT TYPE: LOGICAL DEFAULT: FALSE OPTIONS: FALSE (or 0) Do not apply long-range correction. TRUE (or 1) Add 100% long-range Hartree-Fock exchange to the requested functional. RECOMMENDATION: The$rem variable OMEGA must also be specified, in order to set the range-separation parameter.

MAGNET
Activate the magnetic property module.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE (or 0) Don’t activate the magnetic property module. TRUE (or 1) Activate the magnetic property module.
RECOMMENDATION:
None.

MANY_BODY_INT
Perform a MBE calculation.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
TRUE Perform a MBE calculation. FALSE Do not perform a MBE calculation.
RECOMMENDATION:
NONE

MAX_CIS_CYCLES
Maximum number of CIS iterative cycles allowed.
TYPE:
INTEGER
DEFAULT:
30
OPTIONS:
$n$ User-defined number of cycles.
RECOMMENDATION:
Default is usually sufficient.

MAX_CIS_SUBSPACE
Maximum number of subspace vectors allowed in the CIS iterations
TYPE:
INTEGER
DEFAULT:
As many as required to converge all roots
OPTIONS:
$n$ User-defined number of subspace vectors
RECOMMENDATION:
The default is usually appropriate, unless a large number of states are requested for a large molecule. The total memory required to store the subspace vectors is bounded above by $2nOV$, where $O$ and $V$ represent the number of occupied and virtual orbitals, respectively. $n$ can be reduced to save memory, at the cost of a larger number of CIS iterations. Convergence may be impaired if $n$ is not much larger than CIS_N_ROOTS.

MAX_DIIS_CYCLES
The maximum number of DIIS iterations before switching to (geometric) direct minimization when SCF_ALGORITHM is DIIS_GDM or DIIS_DM. See also THRESH_DIIS_SWITCH.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
1 Only a single Roothaan step before switching to (G)DM $n$ $n$ DIIS iterations before switching to (G)DM.
RECOMMENDATION:
None

MAX_RCA_CYCLES
The maximum number of RCA iterations before switching to DIIS when SCF_ALGORITHM is RCA_DIIS.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
N N RCA iterations before switching to DIIS
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.

MBDVDW
Flag to switch on the MBD-vdW method
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 Do not calculate MBD. 1 Calculate the MBD-vdW contribution to the energy. 2 Calculate the MBD-vdW contribution to the energy and the gradient.
RECOMMENDATION:
NONE

MECP_METHODS
Determines which method to be used.
TYPE:
STRING
DEFAULT:
BRANCHING_PLANE
OPTIONS:
BRANCHING_PLANE Use the branching-plane updating method. MECP_DIRECT Use the direct method. PENALTY_FUNCTION Use the penalty-constrained method.
RECOMMENDATION:
The direct method is stable for small molecules or molecules with high symmetry. The branching-plane updating method is more efficient for larger molecules but does not work if the two states have different symmetries. If using the branching-plane updating method, GEOM_OPT_COORDS must be set to 0 in the $rem section, as this algorithm is available in Cartesian coordinates only. The penalty-constrained method converges slowly and is suggested only if other methods fail. MECP_OPT Determines whether we are doing MECP optimizations. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Do MECP optimization. FALSE Do not do MECP optimization. RECOMMENDATION: None. MECP_PROJ_HESS Determines whether to project out the coupling vector from the Hessian when using branching plane updating method. TYPE: LOGICAL DEFAULT: TRUE OPTIONS: TRUE FALSE RECOMMENDATION: Use the default. MECP_STATE1 Sets the first Born-Oppenheimer state for MECP optimization. TYPE: INTEGER/INTEGER ARRAY DEFAULT: None OPTIONS: [$i$,$j$] Find the $j$th excited state with the total spin $i$; $j=0$ means the SCF ground state. RECOMMENDATION: $i$ is ignored for restricted calculations; for unrestricted calculations, $i$ can only be 0 or 1. MECP_STATE2 Sets the second Born-Oppenheimer state for MECP optimization. TYPE: INTEGER/INTEGER ARRAY DEFAULT: None OPTIONS: [$i$,$j$] Find the $j$th excited state with the total spin $i$; $j=0$ means the SCF ground state. RECOMMENDATION: $i$ is ignored for restricted calculations; for unrestricted calculations, $i$ can only be 0 or 1. MEM_STATIC Sets the memory for AO-integral evaluations and their transformations in Q-Chem 4.1 or older versions. TYPE: INTEGER DEFAULT: 64 corresponding to 64 MB. OPTIONS: $n$ User-defined number of megabytes. RECOMMENDATION: For RI-MP2 calculations using Q-Chem 4.1 or older versions, $150(ON+V)$ of MEM_STATIC is required. Because a number of matrices with $N^{2}$ size also need to be stored, 32–160 MB of additional MEM_STATIC is needed. MEM_TOTAL Sets the total memory available to Q-Chem, in megabytes. TYPE: INTEGER DEFAULT: 2000 2 GB OPTIONS: $n$ User-defined number of megabytes. RECOMMENDATION: Use the default, or set to the physical memory of your machine. The minimum requirement is $3X^{2}$. METECO Sets the threshold criteria for discarding shell-pairs. TYPE: INTEGER DEFAULT: 2 Discard shell-pairs below $10^{-\mathrm{THRESH}}$. OPTIONS: 1 Discard shell-pairs four orders of magnitude below machine precision. 2 Discard shell-pairs below 10${}^{-\mathrm{THRESH}}$. RECOMMENDATION: Use the default. 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.; one of the correlated methods listed in Sections 7.8, 7.9, and 7.7; RECOMMENDATION: In general, consult the literature to guide your selection. Our recommendations for DFT are indicated in bold in Section 5.3.4. MGC_AMODEL Choice of approximate cluster model. TYPE: INTEGER DEFAULT: Determines how the CC equations are approximated: OPTIONS: 0 Local Active-Space Amplitude iterations (pre-calculate GVB orbitals with your method of choice (RPP is good)). 7 Optimize-Orbitals using the VOD 2-step solver. (Experimental-only use with MGC_AMPS = 2, 24 ,246) 8 Traditional Coupled Cluster up to CCSDTQPH. 9 MR-CC version of the Pair-Models. (Experimental) RECOMMENDATION: None MGC_AMPS Choice of Amplitude Truncation TYPE: INTEGER DEFAULT: None OPTIONS: 2$\leq$ n $\leq$ 123456, a sorted list of integers for every amplitude which will be iterated. Choose 1234 for PQ and 123456 for PH RECOMMENDATION: None MGC_LOCALINTER Pair filter on an intermediate. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: Any nonzero value enforces the pair constraint on intermediates, significantly reducing computational cost. Not recommended for $\leq$ 2 pair locality RECOMMENDATION: None MGC_LOCALINTS Pair filter on an integrals. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: Enforces a pair filter on the 2-electron integrals, significantly reducing computational cost. Generally useful. for more than 1 pair locality. RECOMMENDATION: None MGC_NLPAIRS Number of local pairs on an amplitude. TYPE: INTEGER DEFAULT: None OPTIONS: Must be greater than 1, which corresponds to the PP model. 2 for PQ, and 3 for PH. RECOMMENDATION: None MGEMM_THRESH Sets MGEMM threshold to determine the separation between “large” and “small” matrix elements. A larger threshold value will result in a value closer to the single-precision result. Note that the desired factor should be multiplied by 10000 to ensure an integer value. TYPE: INTEGER DEFAULT: 10000 (corresponds to 1) OPTIONS: $n$ User-specified threshold RECOMMENDATION: For small molecules and basis sets up to triple-$\zeta$, the default value suffices to not deviate too much from the double-precision values. Care should be taken to reduce this number for larger molecules and also larger basis-sets. MI_ACTIVE_FRAGMENT Sets the active fragment TYPE: INTEGER DEFAULT: NO DEFAULT OPTIONS: $n$ Specify the fragment on which the TDDFT calculation is to be performed, for LEA-TDDFT(MI). RECOMMENDATION: None MI_LEA Controls the LEA-TDDFT(MI) methods TYPE: INTEGER DEFAULT: NO DEFAULT OPTIONS: 0 The LEA0 method 1 The LEA-Q method 2 The LEAc method RECOMMENDATION: 1 MM_CHARGES Requests the calculation of multipole-derived charges (MDCs). TYPE: LOGICAL DEFAULT: FALSE OPTIONS: TRUE Calculates the MDCs and also the traceless form of the multipole moments RECOMMENDATION: Set to TRUE if MDCs or the traceless form of the multipole moments are desired. The calculation does not take long. MM_SUBTRACTIVE Specifies whether a subtractive scheme is used in the $E_{\mathrm{Coul}}$, Eq. (12.38), portion of the calculation. TYPE: LOGICAL DEFAULT: FALSE OPTIONS: FALSE Only pairs that are not 1-2, 1-3, or 1-4 pairs are used. TRUE All pairs are calculated, and then the pairs that are double counted (1-2, 1-3, and 1-4) are subtracted out. RECOMMENDATION: When running QM/MM or MM calculations there is not recommendation. When running a QM/MM-Ewald calculation the value must be set to TRUE. MODEL_SYSTEM_CHARGE Specifies the QM subsystem charge if different from the$molecule section.
TYPE:
INTEGER
DEFAULT:
NONE
OPTIONS:
$n$ The charge of the QM subsystem.
RECOMMENDATION:
This option only needs to be used if the QM subsystem (model system) has a charge that is different from the total system charge.

MODEL_SYSTEM_MULT
Specifies the QM subsystem multiplicity if different from the \$molecule section.
TYPE:
INTEGER
DEFAULT:
NONE
OPTIONS:
$n$ The multiplicity of the QM subsystem.
RECOMMENDATION:
This option only needs to be used if the QM subsystem (model system) has a multiplicity that is different from the total system multiplicity. ONIOM calculations must be closed shell.

MODE_COUPLING
Number of modes coupling in the third and fourth derivatives calculation.
TYPE:
INTEGER
DEFAULT:
2 for two modes coupling.
OPTIONS:
$n$ for $n$ modes coupling, Maximum value is 4.
RECOMMENDATION:
Use the default.

MOLDEN_FORMAT
Requests a MolDen-formatted input file containing information from a Q-Chem job.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE Append MolDen input file at the end of the Q-Chem output file.
RECOMMENDATION:
None.

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.54

MOM_PRINT
Switches printing on within the MOM procedure.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE Printing is turned off TRUE Printing is turned on.
RECOMMENDATION:
None

MOM_START
Determines when MOM is switched on to stabilize DIIS iterations.
TYPE:
INTEGER
DEFAULT:
0 (FALSE)
OPTIONS:
0 (FALSE) MOM is not used $n$ MOM begins on cycle $n$.
RECOMMENDATION:
Set to 1 if preservation of initial orbitals is desired. If MOM is to be used to aid convergence, an SCF without MOM should be run to determine when the SCF starts oscillating. MOM should be set to start just before the oscillations.

MOPROP_CONV_1ST
Sets the convergence criteria for CPSCF and 1st order TDSCF.
TYPE:
INTEGER
DEFAULT:
6
OPTIONS:
$n<10$ Convergence threshold set to $10^{-n}$.
RECOMMENDATION:
None

MOPROP_CONV_2ND
Sets the convergence criterion for second-order TDSCF.
TYPE:
INTEGER
DEFAULT:
6
OPTIONS:
$n<10$ Convergence threshold set to $10^{-n}$.
RECOMMENDATION:
None

MOPROP_DIIS_DIM_SS
Specified the DIIS subspace dimension.
TYPE:
INTEGER
DEFAULT:
20
OPTIONS:
0 No DIIS. $n$ Use a subspace of dimension $n$.
RECOMMENDATION:
None

MOPROP_DIIS
Controls the use of Pulay’s DIIS in solving the CPSCF equations.
TYPE:
INTEGER
DEFAULT:
5
OPTIONS:
0 Turn off DIIS. 5 Turn on DIIS.
RECOMMENDATION:
None

MOPROP_ISSC_PRINT_REDUCED
Specifies whether the isotope-independent reduced coupling tensor $\mathbf{K}$ should be printed in addition to the isotope-dependent $\mathbf{J}$-tensor when calculating indirect nuclear spin-spin couplings.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE Do not print $\mathbf{K}$. TRUE Print $\mathbf{K}$.
RECOMMENDATION:
None

MOPROP_ISSC_SKIP_DSO
Specifies whether to skip the calculation of the diamagnetic spin-orbit contribution to the indirect nuclear spin-spin coupling tensor.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE Calculate diamagnetic spin-orbit contribution. TRUE Skip diamagnetic spin-orbit contribution.
RECOMMENDATION:
None

MOPROP_ISSC_SKIP_FC
Specifies whether to skip the calculation of the Fermi contact contribution to the indirect nuclear spin-spin coupling tensor.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE Calculate Fermi contact contribution. TRUE Skip Fermi contact contribution.
RECOMMENDATION:
None

MOPROP_ISSC_SKIP_PSO
Specifies whether to skip the calculation of the paramagnetic spin-orbit contribution to the indirect nuclear spin-spin coupling tensor.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE Calculate paramagnetic spin-orbit contribution. TRUE Skip paramagnetic spin-orbit contribution.
RECOMMENDATION:
None

MOPROP_ISSC_SKIP_SD
Specifies whether to skip the calculation of the spin-dipole contribution to the indirect nuclear spin-spin coupling tensor.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE Calculate spin-dipole contribution. TRUE Skip spin-dipole contribution.
RECOMMENDATION:
None

MOPROP_MAXITER_1ST
The maximum number of iterations for CPSCF and first-order TDSCF.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
$n$ Set maximum number of iterations to $n$.
RECOMMENDATION:
Use the default.

MOPROP_MAXITER_2ND
The maximum number of iterations for second-order TDSCF.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
$n$ Set maximum number of iterations to $n$.
RECOMMENDATION:
Use the default.

MOPROP_PERTNUM
Set the number of perturbed densities that will to be treated together.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 All at once. $n$ Treat the perturbed densities batch-wise.
RECOMMENDATION:
Use the default. For large systems, limiting this number may be required to avoid memory exhaustion.

MOPROP_RESTART
Specifies the option for restarting MOProp calculations.
TYPE:
INTEGER
DEFAULT: