7.8 Correlated Excited State Methods: The CIS(D) Family

7.8.5 CIS(D) Job Control and Examples

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(D0) do not depend on the coupled-cluster routines. Users who will not use this legacy CIS(D) method may skip to Section 7.8.6.

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:
       [i,j,k] Find i excited states in the first irrep, j 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:
       [i,j,k] Find i excited states in the first irrep, j 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:
       [i,j,k] Find i excited states in the first irrep, j 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:
       [i,j,k] Find i SF states in the first irrep, j 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:
       [i,j] optimize the jth state of the ith 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 C1 symmetry, i.e., as [1,N] where N is the number of state to optimize (the states are numbered from 1).

Example 7.26  CIS(D) excitation energy calculation for ozone at the experimental ground state geometry C2v

$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 2 lowest triplets in each irrep.
   CCMAN2             false
$end

Example 7.27  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 7.28  CIS(D) excitation energy and transition property calculation (between all states) for ozone at the experimental ground state geometry C2v

$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
   CCMAN2             FALSE
$end