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(May 16, 2021)

The legacy CIS(D) algorithm in Q-Chem is handled by the CCMAN/CCMAN2
modules of Q-Chem’s and shares many of the *$rem* options.
RI-CIS(D), SOS-CIS(D), and SOS-CIS(D${}_{0}$) do not depend on the coupled-cluster
routines. Users who will not use this legacy CIS(D) method may skip to
Section 7.9.6.

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 6.10.8).

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:

$[i,j,k\mathrm{\dots}]$
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:

$[i,j,k\mathrm{\dots}]$
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:

$[i,j,k\mathrm{\dots}]$
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:

$[i,j,k\mathrm{\dots}]$
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 $j$th state of the $i$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 ${C}_{\mathrm{1}}$ symmetry, *i.e.*,
as [1,N] where N is the number of state to optimize (the states are numbered
from 1).

$molecule 0 1 O O 1 RE O 2 RE 1 A RE = 1.272 A = 116.8 $end $rem 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

$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

$molecule 0 1 O O 1 RE O 2 RE 1 A RE = 1.272 A = 116.8 $end $rem 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