EOM-CC(2,3) is invoked by METHOD=EOM-CC(2,3). The following options are available:
EOM_PRECONV_SD
EOM_PRECONV_SD
Solves the EOM-CCSD equations, prints energies, then uses EOM-CCSD vectors
as initial vectors in EOM-CC(2,3). Very convenient for calculations using energy additivity schemes.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
n
Do n SD iterations
RECOMMENDATION:
Turning this option on is recommended
CC_REST_AMPL
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_TRIPLES
CC_REST_TRIPLES
Restricts R3 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_OCC
CC_REST_OCC
Sets the number of restricted occupied orbitals including frozen occupied
orbitals.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
n
Restrict n occupied orbitals.
RECOMMENDATION:
None
CC_REST_VIR
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
To select the active space, orbitals can be reordered by specifying the new order in the $reorder_mosection. The section consists of two rows of numbers (α and β sets), starting from 1, and ending with n, where n is the number of the last orbital specified.
The following example $reorder_mo section shows orbitals 16 and 17 swapped for both α and β electrons:
$reorder_mo 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 16 $end
Example 7.134 EOM-SF(2,3) calculations of methylene.
$molecule 0 3 C H 1 CH H 1 CH 2 HCH CH = 1.07 HCH = 111.0 $end $rem METHOD eom-cc(2,3) BASIS 6-31G SF_STATES [2,0,0,2] N_FROZEN_CORE 1 N_FROZEN_VIRTUAL 1 EOM_PRECONV_SD 20 Get EOM-CCSD energies first (max_iter=20). $end
Example 7.135 This is active-space EOM-SF(2,3) calculations for methane with an elongated CC bond. HF MOs should be reordered as specified in the $reorder_mosection such that active space for triples consists of sigma and sigma* orbitals.
$molecule 0 3 C H 1 CH H 1 CHX 2 HCH H 1 CH 2 HCH 3 A120 H 1 CH 2 HCH 4 A120 CH = 1.086 HCH = 109.4712206 A120 = 120. CHX = 1.8 $end $rem METHOD eom-cc(2,3) BASIS 6-31G* SF_STATES [1,0] N_FROZEN_CORE 1 EOM_PRECONV_SD 20 does eom-ccsd first, max_iter=20 CC_REST_TRIPLES 1 triples are restricted to the active space only CC_REST_AMPL 0 ccsd and eom singles and doubles are full-space CC_REST_OCC 4 specifies active space CC_REST_VIR 17 specifies active space PRINT_ORBITALS 10 (number of virtuals to print) $end $reorder_mo 1 2 5 4 3 1 2 3 4 5 $end
Example 7.136 EOM-IP-CC(2,3) calculation of three lowest electronic states of water cation.
$molecule 0 1 H 0.774767 0.000000 0.458565 O 0.000000 0.000000 -0.114641 H -0.774767 0.000000 0.458565 $end $rem METHOD eom-cc(2,3) BASIS 6-311G IP_STATES [1,0,1,1] $end