# 7.8.20 Job Control for EOM-CC(2,3)

EOM-CC(2,3) is invoked by METHOD=EOM-CC(2,3). The following options are available:

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
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
Restricts $R_{3}$ 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
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
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 $reorder_mosection. The section consists of two rows of numbers ($\alpha$ and $\beta$ 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 $\alpha$ and $\beta$ 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


## 7.8.20.1 Examples

Example 7.71  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 7.72  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 7.73 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