The legacy CIS(D) algorithm in Q-Chem is handled by the CCMAN/CCMAN2 modules of Q-Chem’s and shares many of the $rem options. RI-CIS(D), SOS-CIS(D), and SOS-CIS(D) do not depend on the coupled-cluster routines. Users who will not use this legacy CIS(D) method may skip to Section 7.7.6.
As with all post-HF calculations, it is important to ensure there are sufficient resources available for the necessary integral calculations and transformations. For CIS(D), these resources are controlled using the $rem variables CC_MEMORY, MEM_STATIC and MEM_TOTAL (see Section 6.8.7).
To request a CIS(D) calculation the METHOD $rem should be set to CIS(D) and the number of excited states to calculate should be specified by EE_STATES (or EE_SINGLETS and EE_TRIPLETS when appropriate). Alternatively, CIS(D) will be performed when EXCHANGE = HF, CORRELATION = CI and EOM_CORR = CIS(D). The SF-CIS(D) is invoked by using SF_STATES.
EE_STATES
Sets the number of excited state roots to find. For closed-shell reference,
defaults into EE_SINGLETS. For open-shell references, specifies all
low-lying states.
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0
Do not look for any excited states.
OPTIONS:
Find excited states in the first irrep,
states in the second irrep etc.
RECOMMENDATION:
None
EE_SINGLETS
Sets the number of singlet excited state roots to find. Valid only
for closed-shell references.
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0
Do not look for any excited states.
OPTIONS:
Find excited states in the first irrep, states
in the second irrep etc.
RECOMMENDATION:
None
EE_TRIPLETS
Sets the number of triplet excited state roots to find. Valid only
for closed-shell references.
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0
Do not look for any excited states.
OPTIONS:
Find excited states in the first irrep, states
in the second irrep etc.
RECOMMENDATION:
None
SF_STATES
Sets the number of spin-flip target states roots to find.
TYPE:
INTEGER/INTEGER ARRAY
DEFAULT:
0
Do not look for any spin-flip states.
OPTIONS:
Find SF states in the first irrep, states
in the second irrep etc.
RECOMMENDATION:
None
Note: It is a symmetry of a transition rather than that of a target state that is specified in excited state calculations. The symmetry of the target state is a product of the symmetry of the reference state and the transition. For closed-shell molecules, the former is fully symmetric and the symmetry of the target state is the same as that of transition, however, for open-shell references this is not so.
CC_STATE_TO_OPT
Specifies which state to optimize.
TYPE:
INTEGER ARRAY
DEFAULT:
None
OPTIONS:
[,]
optimize the th state of the th irrep.
RECOMMENDATION:
None
Note: Since there are no analytic gradients for CIS(D), the symmetry should be turned off for geometry optimization and frequency calculations, and CC_STATE_TO_OPT should be specified assuming symmetry, i.e., as [1,N] where N is the number of state to optimize (the states are numbered from 1).
Example 7.22 CIS(D) excitation energy calculation for ozone at the experimental ground state geometry
$molecule 0 1 O O 1 RE O 2 RE 1 A RE = 1.272 A = 116.8 $end $rem JOBTYPE SP METHOD CIS(D) BASIS 6-31G* N_FROZEN_CORE 3 use frozen core EE_SINGLETS [2,2,2,2] find 2 lowest singlets in each irrep. EE_TRIPLETS [2,2,2,2] find two lowest triplets in each irrep. $end
Example 7.23 CIS(D) geometry optimization for the lowest triplet state of water. The symmetry is automatically turned off for finite difference calculations
$molecule 0 1 o h 1 r h 1 r 2 a r 0.95 a 104.0 $end $rem JOBTYPE opt BASIS 3-21g METHOD cis(d) EE_TRIPLETS 1 calculate one lowest triplet CC_STATE_TO_OPT [1,1] optimize the lowest state (1st state in 1st irrep) $end
Example 7.24 CIS(D) excitation energy and transition property calculation (between all states) for ozone at the experimental ground state geometry
$molecule 0 1 O O 1 RE O 2 RE 1 A RE = 1.272 A = 116.8 $end $rem JOBTYPE SP BASIS 6-31G* PURCAR 2 Non-spherical (6D) METHOD CIS(D) EE_SINGLETS [2,2,2,2] EE_TRIPLETS [2,2,2,2] CC_TRANS_PROP 1 $end