6.20 Incremental Correlation Methods

6.20.2 Job Control for iFCI

(May 16, 2021)

IFCI_TUPLES
       Level of n-body expansion to solve. Note that n>2 can be computationally costly.
TYPE:
       INTEGER
DEFAULT:
       Must be set.
OPTIONS:
       1 n=1 2 n=2 3 n=3 4 n=4
RECOMMENDATION:
       Use n=2 for initial system analysis, n>2 for higher accuracy.

IFCI_READ
       Restarts iFCI with existing TUPLES_1E_DATA file, if it exists.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Start from scratch 1 Restart from previous file
RECOMMENDATION:
       Use 0 if no previous run files exist. Use 1 if intending to restart from previous data.

IFCI_TRIPLETS
       Set state to solve.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       0 Singlet 1 Triplet 2 Quintet
RECOMMENDATION:
       None

IFCI_ZETA
       Convergence for each iFCI increment. Note that the format is ζ= IFCI_ZETA/10.
TYPE:
       INTEGER
DEFAULT:
       55
OPTIONS:
       45 Loose 55 Moderate 65 Tight 75 Tighter 85 Quite tight 95 Maximum
RECOMMENDATION:
       Use 65 and increase to 75 to check convergence.

HBCI_EPS1
       Determines dimension of HBCI space.
TYPE:
       INTEGER
DEFAULT:
       1000
OPTIONS:
       N HBCI ε1 in μ Eh
RECOMMENDATION:
       Use default or 500 for tighter convergence.

IFCI_TUPLE_THRESH
       Collapse near-degenerate geminals within threshold into one body.
TYPE:
       INTEGER
DEFAULT:
       2500
OPTIONS:
       n in μEh
RECOMMENDATION:
       Use default unless there are sets of highly correlating occupied orbitals.

IFCI_TRIPLES_SCREEN
       Cutoff (𝒞3) for determining if a 3-body term is significant.
TYPE:
       INTEGER
DEFAULT:
       1000
OPTIONS:
       n where 𝒞3=10-ζ×n in Eh
RECOMMENDATION:
       Use the default unless looser (higher n) or tighter (lower n) consideration of triads for a given system is desired. Setting to 0 computes all triads (costly).

IFCI_QUAD_SCREEN
       Cutoff (𝒞4) for determining if a 4-body term is significant.
TYPE:
       INTEGER
DEFAULT:
       IFCI_TRIPLES_SCREEN
OPTIONS:
       n where 𝒞4=10-ζ×n in Eh
RECOMMENDATION:
       Same as IFCI_TRIPLES_SCREEN but note that 4-body terms are significantly more costly.

IFCI_STATE_ADD
       Adds additional states to HBCI solver when there is degeneracy amongst states.
TYPE:
       INTEGER
DEFAULT:
       10
OPTIONS:
       n Add states within n mEh
RECOMMENDATION:
       Use default unless it is known that degenerate states are present.

IFCI_PRINT
       Larger number gives more output.
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       1 Minimal output 2 Readable output 3 Extra output 4 Excessive output 5+ Bug testing output
RECOMMENDATION:
       2 is recommended, 1-3 is appropriate, larger than 4 is unnecessary (consider yourself warned).

IFCI_NO_THRESH
       Equivalent to HBCI ε1 for increment-specific NO generation step.
TYPE:
       INTEGER
DEFAULT:
       1000
OPTIONS:
       n in μEh
RECOMMENDATION:
       Set to equal HBCI_EPS1.

IFCI_REF_ITER
       Use HF or PP reference density.
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       0 HF 1 PP
RECOMMENDATION:
       Use 0.

IFCI_OCC
       Specifies the number of active occupied orbitals.
TYPE:
       INTEGER
DEFAULT:
       Full valence.
OPTIONS:
       n Include n orbitals in the active space -1 Full valence
RECOMMENDATION:
       Use full valence active space.