Input for time-dependent density functional theory calculations follows very closely the input already described for the uncorrelated excited state methods described in the previous section (in particular, see Section 7.2.8). There are several points to be aware of:
The exchange and correlation functionals are specified exactly as for a ground state DFT calculation, through EXCHANGE and CORRELATION.
If RPA is set to TRUE, a “full” TDDFT calculation will be performed, however the default value is RPA = FALSE, which invokes the TDA,470 in which the de-excitation amplitudes in Eq. (7.15) are neglected, which is usually a good approximation for excitation energies, although oscillator strengths within the TDA no longer formally satisfy the Thomas-Reiche-Kuhn sum rule.174 For RPA = TRUE, a TDA calculation is performed first and used as the initial guess for the full TDDFT calculation. The TDA calculation can be skipped altogether using RPA = 2
If SPIN_FLIP is set to TRUE when performing a TDDFT calculation, a SF-DFT calculation will also be performed. At present, SF-DFT is only implemented within TDDFT/TDA so RPA must be set to FALSE. Remember to set the spin multiplicity to 3 for systems with an even-number of electrons (e.g., diradicals), and 4 for odd-number electron systems (e.g., triradicals).
If MGGA_GINV is set to 1 when performing a TDDFT calculation, gauge invariance correction will be added to MGGA functionals. 68
TRNSS
TRNSS
Controls whether reduced single excitation space is used.
TYPE:
LOGICAL
DEFAULT:
FALSE
Use full excitation space.
OPTIONS:
TRUE
Use reduced excitation space.
RECOMMENDATION:
None
TRTYPE
TRTYPE
Controls how reduced subspace is specified.
TYPE:
INTEGER
DEFAULT:
1
OPTIONS:
1
Select orbitals localized on a set of atoms.
2
Specify a set of orbitals.
3
Specify a set of occupied orbitals, include excitations to all virtual orbitals.
RECOMMENDATION:
None
MGGA_GINV
MGGA_GINV
Controls whether to add gauge invariance correction to MGGA functionals.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0
No correction.
1
Add gauge invariance correction to MGGA functionals.
RECOMMENDATION:
Not recommended when TDA is used because TDA has broken gauge invariance.
N_SOL
N_SOL
Specifies number of atoms or orbitals in the $solute section.
TYPE:
INTEGER
DEFAULT:
No default.
OPTIONS:
User defined.
RECOMMENDATION:
None
CISTR_PRINT
CISTR_PRINT
Controls level of output.
TYPE:
LOGICAL
DEFAULT:
FALSE
Minimal output.
OPTIONS:
TRUE
Increase output level.
RECOMMENDATION:
None
CUTOCC
CUTOCC
Specifies occupied orbital cutoff.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
0-200
CUTOFF = CUTOCC/100
RECOMMENDATION:
None
CUTVIR
CUTVIR
Specifies virtual orbital cutoff.
TYPE:
INTEGER
DEFAULT:
0
No truncation
OPTIONS:
0-100
CUTOFF = CUTVIR/100
RECOMMENDATION:
None
PBHT_ANALYSIS
PBHT_ANALYSIS
Controls whether overlap analysis of electronic excitations is performed.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE
Do not perform overlap analysis.
TRUE
Perform overlap analysis.
RECOMMENDATION:
None
PBHT_FINE
PBHT_FINE
Increases accuracy of overlap analysis.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE
TRUE
Increase accuracy of overlap analysis.
RECOMMENDATION:
None
SRC_DFT
SRC_DFT
Selects form of the short-range corrected functional.
TYPE:
INTEGER
DEFAULT:
No default
OPTIONS:
1
SRC1 functional.
2
SRC2 functional.
RECOMMENDATION:
None
OMEGA
OMEGA
Sets the Coulomb attenuation parameter for the short-range component.
TYPE:
INTEGER
DEFAULT:
No default
OPTIONS:
Corresponding to , in units of bohr
RECOMMENDATION:
None
OMEGA2
OMEGA2
Sets the Coulomb attenuation parameter for the long-range component.
TYPE:
INTEGER
DEFAULT:
No default
OPTIONS:
Corresponding to , in units of bohr
RECOMMENDATION:
None
HF_SR
HF_SR
Sets the fraction of Hartree-Fock exchange at .
TYPE:
INTEGER
DEFAULT:
No default
OPTIONS:
Corresponding to HF_SR =
RECOMMENDATION:
None
HF_LR
HF_LR
Sets the fraction of Hartree-Fock exchange at .
TYPE:
INTEGER
DEFAULT:
No default
OPTIONS:
Corresponding to HF_LR =
RECOMMENDATION:
None
WANG_ZIEGLER_KERNEL
WANG_ZIEGLER_KERNEL
Controls whether to use the Wang-Ziegler non-collinear exchange-correlation
kernel in a SF-DFT calculation. Set NEW_DFT = true if using a Q-Chem version older than 5.0.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE
Do not use non-collinear kernel.
TRUE
Use non-collinear kernel.
RECOMMENDATION:
None
SET_CISGUES
SET_CISGUES
Controls how to generate the initial guess excitation vectors in CIS/TDA/RPA calculations.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0
Generate N (no. of roots requested) occupiedvirtual single orbital transitions according to their orbital energy difference order (from low to high). This is the common scenario.
1
Generate N-1 occupiedvirtual single orbital transitions according to their orbital energy difference order (from low to high), and generate another guess excitation vector consist of all the remaining single orbital transitions in the occupiedvirtual transition space with equal weights.
2
Generate N occupied/virtual single orbital transitions according to their orbital energy difference order (from low to high), and generate one more guess excitation vector consist of all the remaining single orbital transitions in the occupiedvirtual transition space with equal weights.
RECOMMENDATION:
The default setting should work for most of the cases. However, when the no. of roots is small, in some CIS/TDA/RPA calculations low energy excited states could be missing. The options SET_CISGUES = 1 or 2 may remedy this root missing issue by sampling more vectors in the transition space. Setting SET_CISGUES = 1 or 2 may take more cycles to converge in the Davidson iteration, but the results are expected to be more reliable. Currently SET_CISGUES = 1 or 2 are not supported in SF-XCIS calculations. Setting TRNSS = TRUE also disables the setting of SET_CISGUES.