# 7.10.5 Job Control for the RASCI1 Implementation

At present the RASCI1 and RASCI2 implementations employ different keywords (which will be reconciled in a future version). This subsection applies to RASCI1 (even electron systems, spin adapted algorithm using exact integrals).

The use of the RAS-CI1 methodology is controlled by setting the \$rem variable CORRELATION to RASCI and EXCHANGE should be set to HF. The RASCI1 implementation is only compatible with even numbers of electrons and restricted orbitals, i.e., UNRESTRICTED = FALSE.

The minimum input also requires specifying the desired (non-zero) value for RAS_ROOTS, the number of electrons in the “active” RAS2 space and the number of orbitals in RAS1 and RAS2 subspaces.

RAS_ROOTS
Sets the number of RAS-CI roots to be computed.
TYPE:
INTEGER
DEFAULT:
None
OPTIONS:
$n$ $n>0$ Compute $n$ RAS-CI states
RECOMMENDATION:
None. Only works with RASCI.

RAS_ELEC
Sets the number of electrons in RAS2 (active electrons).
TYPE:
INTEGER
DEFAULT:
None
OPTIONS:
$n$ User-defined integer, $n>0$
RECOMMENDATION:
None. Only works with RASCI.

RAS_ACT
Sets the number of orbitals in RAS2 (active orbitals).
TYPE:
INTEGER
DEFAULT:
None
OPTIONS:
$n$ User-defined integer, $n>0$
RECOMMENDATION:
None. Only works with RASCI.

RAS_OCC
Sets the number of orbitals in RAS1
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$n$ User-defined integer, $n>0$
RECOMMENDATION:
These are the initial doubly occupied orbitals (RAS1) before including $hole$ type of excitations. The RAS1 space starts from the lowest orbital up to RAS_OCC, i.e. no frozen orbitals option available yet. Only works with RASCI.

RAS_DO_HOLE
Controls the presence of hole excitations in the RAS-CI wave function.
TYPE:
LOGICAL
DEFAULT:
TRUE
OPTIONS:
TRUE Include hole configurations (RAS1 to RAS2 excitations) FALSE Do not include hole configurations
RECOMMENDATION:
None. Only works with RASCI.

RAS_DO_PART
Controls the presence of particle excitations in the RAS-CI wave function.
TYPE:
LOGICAL
DEFAULT:
TRUE
OPTIONS:
TRUE Include particle configurations (RAS2 to RAS3 excitations) FALSE Do not include particle configurations
RECOMMENDATION:
None. Only works with RASCI.

RAS_AMPL_PRINT
Defines the absolute threshold ($\times 10^{2}$) for the CI amplitudes to be printed.
TYPE:
INTEGER
DEFAULT:
10 0.1 minimum absolute amplitude
OPTIONS:
$n$ User-defined integer, $n\geq 0$
RECOMMENDATION:
None. Only works with RASCI.

RAS_ACT_ORB
Sets the user-selected active orbitals (RAS2 orbitals).
TYPE:
INTEGER ARRAY
DEFAULT:
From RAS_OCC+1 to RAS_OCC+RAS_ACT
OPTIONS:
$[i,j,k...]$ The number of orbitals must be equal to the RAS_ACT variable
RECOMMENDATION:
None. Only works with RASCI.

RAS_NATORB
Controls the computation of the natural orbital occupancies.
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE Compute natural orbital occupancies for all states FALSE Do not compute natural orbital occupancies
RECOMMENDATION:
None. Only works with RASCI.

RAS_NATORB_STATE
Saves the natural orbitals of the $i$-th RASCI computed state into the .fchk file.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$i$ Saves the natural orbitals for the $i$-th state
RECOMMENDATION:
None. Only works with RASCI and if GUI=2.

RAS_GUESS_CS
Controls the number of closed shell guess configurations in RAS-CI.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$n$ Imposes to start with $n$ closed shell guesses
RECOMMENDATION:
Only relevant for the computation of singlet states. Only works with RASCI.

RAS_SPIN_MULT
Specifies the spin multiplicity of the roots to be computed
TYPE:
INTEGER
DEFAULT:
1 Singlet states
OPTIONS:
0 Compute any spin multiplicity $2n+1$ User-defined integer, $n\geq 0$
RECOMMENDATION:
Only for RASCI, which at present only allows for the computation of systems with an even number of electrons. Thus, RAS_SPIN_MULT only can take odd values.

RAS_PT2
Perform second-order perturbative correction to RAS-CI energy
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE Compute RASCI(2) energy corrections FALSE Do not compute RASCI(2) energy corrections
RECOMMENDATION:
None. Only works with RASCI.

RAS_PT2_PARTITION
Specifies the partitioning scheme in RASCI(2)
TYPE:
INTEGER
DEFAULT:
1 Davidson-Kapuy (DK) partitioning
OPTIONS:
2 Epstein-Nesbet (EN) partitioning 0 Do both DK and EN partitionings
RECOMMENDATION:
Only for RASCI if RAS_PT2 is set to true.

RAS_PT2_VSHIFT
Defines the energy level shift ($\times 10^{3}~{}au$) in RASCI(2)
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$n$ User-defined integer
RECOMMENDATION:
Only for RASCI if RAS_PT2 is set to true.

RAS_SRDFT
Perform short-range density functional RAS-CI calculation
TYPE:
LOGICAL
DEFAULT:
FALSE
OPTIONS:
TRUE Compute RASCI-$sr$DFT states and energies FALSE Do not perform a RASCI-$sr$DFT calculation
RECOMMENDATION:
None. Only works with RASCI. RAS_SRDFT_EXC and RAS_SRDFT_COR need to be set.

RAS_SRDFT_EXC
Define short-range exchange functional
TYPE:
STRING
DEFAULT:
No default
OPTIONS:
NAME Use RAS_SRDFT_EXC = NAME, where NAME is one of the short-range exchange functionals listed in Section 5.3.2
RECOMMENDATION:
None. Only works with RASCI.

RAS_SRDFT_COR
Define short-range correlation functional
TYPE:
STRING
DEFAULT:
No default
OPTIONS:
NAME Use RAS_SRDFT_COR = NAME, where NAME is one of the short-range correlation functionals listed in Section 5.3.3
RECOMMENDATION:
None. Only works with RASCI.

RAS_OMEGA
Sets the Coulomb range-separation parameter within the RAS-CI-$sr$DFT method.
TYPE:
INTEGER
DEFAULT:
400 ($\omega=0.4$ bohr${}^{-1}$)
OPTIONS:
$n$ Corresponding to $\omega=n/1000$, in units of bohr${}^{-1}$
RECOMMENDATION:
None. Range-separation parameter is typical indicated by $\omega$ or $\mu$. Only works with RASCI.

RAS_SRDFT_DAMP
Sets damping factor ($\alpha<1$) in the RAS-CI-$sr$DFT method.
TYPE:
REAL
DEFAULT:
0.5 ($\alpha=0.5$)
OPTIONS:
$\alpha$ Damping factor $0<\alpha<1$
RECOMMENDATION:
Modify in case of convergence issues along the RAS-CI-$sr$DFT iterations. Only works with RASCI

RAS_SRDFT_SA_ROOTS
Sets the list of roots used to build the state averaged reference density in RAS-CI-srDFT.
TYPE:
INTEGER ARRAY
DEFAULT:
All computed states
OPTIONS:
$[i,j,k\ldots]$ List of states.
RECOMMENDATION:
None. Only works with RASCI

RAS_NFRAG
If $n>0$ activates the excitation analysis in RASCI
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
$n$ Number of fragments to be considered
RECOMMENDATION:
Only for RASCI. The printed information level is controlled by RAS_PRINT

RAS_NFRAG_ATOMS
Sets the number of atoms in each fragment.
TYPE:
INTEGER ARRAY
DEFAULT:
None
OPTIONS:
$[i,j,k...]$ The sum of the numbers must be equal to the total number of atoms in the systems
RECOMMENDATION:
None. Only works with RASCI.

RAS_FRAG_SETS
Sets the number of atoms in each fragment.
TYPE:
INTEGER ARRAY
DEFAULT:
[NOcc,NAct,NVir] Number of orbitals within RAS1, RAS2 and RAS3 spaces
OPTIONS:
$[i,j,k...]$ Defines sets of canonical MOs to be localized into $n$ fragments
RECOMMENDATION:
Setting within RAS1, RAS2 and RAS3 spaces alleviates the computational cost of the localization procedure. It might also result in improved fragment orbitals. Only works with RASCI.