CAS_METHOD
CAS_METHOD
Indicates whether orbital optimization is requested.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0
Not running a CAS calculation
1
CAS-CI (no orbital optimization)
2
CASSCF (orbital optimization)
RECOMMENDATION:
Use 2 for best accuracy, but such computations may become infeasible
for large active spaces.
CAS_M_S
CAS_M_S
The number of unpaired electrons desired in the CAS wavefunction.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
for a wavefunction with unpaired electrons
RECOMMENDATION:
CAS_N_ELEC
CAS_N_ELEC
Specifies the number of active electrons.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
include electrons in the active space
-1
include all electrons in the active space
RECOMMENDATION:
Use the smallest active space possible for the given system.
CAS_N_ORB
CAS_N_ORB
Specifies the number of active orbitals.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
include orbitals in the active space
-1
include all orbitals in the active space
RECOMMENDATION:
Use the smallest active space possible for the given system.
CAS_N_ROOTS
CAS_N_ROOTS
Specifies the number of electronic states to determine.
TYPE:
INTEGER
DEFAULT:
1
OPTIONS:
solve for roots of the Hamiltonian
RECOMMENDATION:
CAS_THRESH
CAS_THRESH
Specifies the threshold for matrix elements to be included in the CAS Hamiltonian.
TYPE:
INTEGER
DEFAULT:
12
OPTIONS:
for a threshold of
RECOMMENDATION:
CAS_SAVE_NAT_ORBS
CAS_SAVE_NAT_ORBS
Save the CAS natural orbitals in place of the reference orbitals.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
TRUE
overwrite the reference orbitals with CAS natural orbitals
FALSE
do not save the CAS natural orbitals
RECOMMENDATION:
MAX_CASSCF_CYCLES
MAX_CASSCF_CYCLES
Maximum number of orbital optimization cycles for CASSCF.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
set maximum number of optimization cycles to
RECOMMENDATION:
CAS_USE_RI
CAS_USE_RI
Indicates whether the resolution of the identity approximation should be used.
TYPE:
BOOLEAN
DEFAULT:
FALSE
OPTIONS:
FALSE
Compute 2-electron integrals analytically
TRUE
Use the RI approximation for 2-electron integrals
RECOMMENDATION:
Analytic integrals are more accurate, RI integrals are faster
CAS_DAVIDSON_TOL
CAS_DAVIDSON_TOL
Specifies the tolerance for the Davidson solver used in CAS.
TYPE:
INTEGER
DEFAULT:
5
OPTIONS:
for a threshold of
RECOMMENDATION:
The default should be suitable in most cases
CAS_DAVIDSON_MAXVECTORS
CAS_DAVIDSON_MAXVECTORS
Specifies the maximum number of vectors to augment the Davidson search space in CAS.
TYPE:
INTEGER
DEFAULT:
10
OPTIONS:
sets the maximum Davidson subspace size to +CAS_N_ROOTS
RECOMMENDATION:
The default should be suitable in most cases
CAS_SOLVER
CAS_SOLVER
Specifies the solver to be used for the active space.
TYPE:
INTEGER
DEFAULT:
1
OPTIONS:
1
CAS-CI/CASSCF
2
ASCI (see Section 6.21)
3
Truncated CI (CIS, CISD, CISDT, etc.)
RECOMMENDATION:
TRUNC_CI_LEVEL
TRUNC_CI_LEVEL
Specifies the order of truncated CI to be used in the active space.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0
Do not carry out truncated CI
1
CIS
2
CISD
3
CISDT
4
CISDTQ
etc.
RECOMMENDATION:
Example 6.45 CASCI(6,14) calculation for the ground state of N.
$molecule 0 1 N 0.0 0.0 0.0 N 0.0 0.0 1.8 $end $rem EXCHANGE hf BASIS cc-pvtz CAS_METHOD 1 ! 1 for CAS-CI, 2 for CASSCF CAS_M_S 0 ! M_s value*2 ASCI_DIAG 2 ! Arma Sparse=0, Davidson=1, Eigen Sparse=2 CAS_N_ELEC 6 ! N_elec CAS_N_ORB 14 ! N_orb CAS_N_ROOTS 1 ! N_roots CAS_SOLVER 1 ! 2=ASCI, 1=Olsen, 0=naive THRESH 14 MAX_SCF_CYCLES 400 SCF_CONVERGENCE 6 MEM_TOTAL 4000 MEM_STATIC 1000 SCF_ALGORITHM diis_gdm INTEGRAL_SYMMETRY false POINT_GROUP_SYMMETRY false $end
Example 6.46 CASSCF(6,6) calculation for the ground state of N.
$molecule 0 1 N 0.0 0.0 0.0 N 0.0 0.0 1.8 $end $rem EXCHANGE hf BASIS cc-pvtz CAS_METHOD 2 !1 for CAS-CI, 2 for CASSCF CAS_M_S 0 !M_s value*2 ASCI_DIAG 2 !Arma Sparse=0, Davidson=1, Eigen Sparse=2 CAS_N_ELEC 6 !N_elec CAS_N_ORB 6 !N_orb CAS_N_ROOTS 1 !N_roots THRESH 14 MAX_SCF_CYCLES 400 SCF_CONVERGENCE 6 MEM_TOTAL 4000 MEM_STATIC 1000 SCF_ALGORITHM diis_gdm INTEGRAL_SYMMETRY false POINT_GROUP_SYMMETRY false $end
Example 6.47 Geometry optimization of the ground state of N at the CASSCF(6,6)/cc-pVTZ level of theory.
$molecule 0 1 N 0.0 0.0 0.0 N 0.0 0.0 1.3 $end $rem JOBTYPE opt EXCHANGE hf BASIS cc-pvtz CAS_METHOD 2 !1 for CAS-CI, 2 for CASSCF CAS_M_S 0 !M_s value*2 ASCI_DIAG 2 !Arma Sparse=0, Davidson=1, Eigen Sparse=2 CAS_N_ELEC 6 !N_elec CAS_N_ORB 6 !N_orb CAS_N_ROOTS 1 !N_roots CAS_SAVE_NAT_ORBS true !overwrite MOs with CAS natural orbs THRESH 14 MAX_SCF_CYCLES 400 SCF_CONVERGENCE 6 MEM_TOTAL 4000 MEM_STATIC 1000 SCF_ALGORITHM diis_gdm INTEGRAL_SYMMETRY false POINT_GROUP_SYMMETRY false $end
Example 6.48 Truncated CI (S, D, T) calculation for the ground state N using the CASCI routines.
$molecule 0 1 N 0.0 0.0 0.0 N 0.0 0.0 1.1 $end $rem EXCHANGE hf BASIS cc-pvdz CAS_METHOD 1 !1 for CAS-CI, 2 for CASSCF CAS_M_S 0 !M_s value*2 ASCI_DIAG 2 !Arma Sparse=0, Davidson=1, Eigen Sparse=2 CAS_N_ELEC 6 !N_elec CAS_N_ORB -1 !N_orb (-1: include all orbitals in active space) CAS_N_ROOTS 1 !N_roots CAS_SOLVER 3 !2=ASCI, 1=Olsen, 0=naive, 3=truncated CI TRUNC_CI_LEVEL 3 !include up to triples excitations THRESH 14 MAX_SCF_CYCLES 400 SCF_CONVERGENCE 6 MEM_TOTAL 4000 MEM_STATIC 1000 SCF_ALGORITHM diis_gdm INTEGRAL_SYMMETRY false POINT_GROUP_SYMMETRY false $end