There is also another approximate method, one-center NOCIS (1C-NOCIS)
916
Phys. Chem. Chem. Phys.
(2020),
22,
pp. 8182.
Link
, which is an intermediate between NOCIS and STEX. The open-shell determinants are separately optimized as in NOCIS, but the coupling between non-orthogonal determinants with core holes on different centers is ignored, and NOCI is used to compute the remaining matrix elements between non-orthogonal determinants. 1C-NOCIS constructs the orthogonal Slater-Condon components of the matrices, and then performs NOCI to obtain the relevant non-orthogonal components. The diagonal blocks are then projected against the ground state. For singlet NOCIS, 1C-NOCIS is the same as STEX, since there are no open-shell ground-state orbitals.
There are two main advantages of 1C-NOCIS. First, it is substantially cheaper to evaluate than NOCIS and so enables the treatment of larger molecules. Second, and in contrast to STEX, it allows the open-shell states to relax separately, which may have a substantial impact on accuracy.
NOCIS, 1C-NOCIS, and STEX run as subroutines in GEN_SCFMAN. Thus, for all calculations, you must set GEN_SCFMAN = TRUE. It is also highly recommended that you run an open-shell ground state calculation prior to running your NOCIS/STEX/1C-NOCIS calculations, which are all restricted.
NOCIS
NOCIS
Requests a NOCIS/STEX/1C-NOCIS/EA-TDDFT calculation.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
FALSE
Do not run these methods.
TRUE
Run one of these methods, options controlled in $nocis.
RECOMMENDATION:
None
Options below this line are set within the $nocis section.
STEX
Run a STEX calculation
INPUT SECTION: $nocis
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
The presence of this keyword will activate STEX.
RECOMMENDATION:
None
ONE_CENTER
Run a 1C-NOCIS calculation
INPUT SECTION: $nocis
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
False
Run a NOCIS calculation.
True
Run a 1C-NOCIS calculation.
RECOMMENDATION:
None
ORB_OFFSET
Determines the starting orbital for a NOCIS/STEX/1C-NOCIS/EA-TDDFT calculation.
INPUT SECTION: $nocis
TYPE:
INTEGER
DEFAULT:
NONE
OPTIONS:
Positive integer
RECOMMENDATION:
Set according to the first orbital of interest in the system in question.
For example, this would be set to 0 for the O K-edge in CO because
the two O 1s orbitals lie below the C 1s, so for the C K-edge this
would be set to 2.
NUM_REF
Sets the number of reference orbitals in a NOCIS/STEX/1C-NOCIS/EA-TDDFT calculation.
INPUT SECTION: $nocis
TYPE:
INTEGER
DEFAULT:
NONE
OPTIONS:
Positive integer
RECOMMENDATION:
Set according to the number of consecutive orbitals of interest for the
calculation. For example, for the oxygen K-edge in CO, the
number of references would be 2 (two O 1s orbitals),
whereas for the carbon K-edge it would be 1 (one C 1s).
Example 7.29 NOCIS for the nitrogen K-edge of N
$molecule 0 1 N 0.000000 0.000000 0.564990 N 0.000000 0.000000 -0.564990 $end $rem METHOD hf BASIS sto-3g UNRESTRICTED false GEN_SCFMAN true NOCIS true THRESH 14 integral_symmetry false point_group_symmetry False MAX_SCF_CYCLES 500 $end ! the default behavior is NOCIS $nocis ORB_OFFSET 0 NUM_REF 2 $end
Example 7.30 STEX for the carbon K-edge of CN
$molecule 0 2 C 0.0000000 0.0000000 -0.6258140 N 0.0000000 0.0000000 0.5364120 $end $rem METHOD hf BASIS sto-3g SCF_GUESS core SCF_ALGORITHM diis_gdm integral_symmetry false point_group_symmetry False MAX_SCF_CYCLES 5000 THRESH 14 SCF_CONVERGENCE 10 $end @@@ $molecule read $end $rem METHOD hf BASIS sto-3g SCF_GUESS read UNRESTRICTED false SCF_ALGORITHM diis_gdm GEN_SCFMAN true NOCIS true integral_symmetry false point_group_symmetry False MAX_SCF_CYCLES 5000 THRESH 14 SCF_CONVERGENCE 10 $end $nocis STEX ORB_OFFSET 1 NUM_REF 1 $end
Example 7.31 1C-NOCIS for the oxygen K-edge of O
$molecule 0 3 O 0.0000000 0.0000000 0.6021380 O 0.0000000 0.0000000 -0.6021380 $end $rem METHOD hf BASIS sto-3g GEN_SCFMAN true THRESH 14 integral_symmetry false point_group_symmetry False MAX_SCF_CYCLES 500 $end @@@ $molecule read $end $rem UNRESTRICTED false SCF_GUESS read METHOD hf BASIS sto-3g GEN_SCFMAN true NOCIS true THRESH 14 integral_symmetry false point_group_symmetry False MAX_SCF_CYCLES 500 $end $nocis ONE_CENTER ORB_OFFSET 0 NUM_REF 2 $end