$DRT/$CIDRT

$DRT group

(required for SCFTYP=MCSCF)
$CIDRT group
(required for CITYP=GUGA)

This group describes the -MCSCF- or -CI- wavefunction. The distinct row table is the means by which the Graphical Unitary Group Approach (GUGA) names the configurations.

The group is spelled DRT for MCSCF runs, and CIDRT for CI runs. The main difference in these is NMCC vs. NFZC.

There is no default for GROUP, and you must choose one of FORS, FOCI, SOCI, or IEXCIT.

GROUP
= the name of the point group to be used. This is usually the same as that in $DATA, except for RUNTYP=HESSIAN, when it must be C1. Choose from the following: C1, C2, CI, CS, C2V, C2H, D2, D2H, C4V, D4, D4H. If your $DATA group is not listed, choose only C1 here.

FORS
= flag specifying the Full Optimized Reaction Space set of configuration should be generated. This is usually set true for MCSCF runs, but if it is not, see FORS in $MCSCF. (Default=.FALSE.)

FOCI
= flag specifying first order CI. In addition to the FORS configurations, all singly excited CSFs from the FORS reference are included. Default=.FALSE.

SOCI
= flag specifying second order CI. In addition to the FORS configurations, all singly and doubly excited configurations from the FORS reference are included. (Default=.FALSE.)

IEXCIT
= electron excitation level, for example 2 will lead to a singles and doubles CI. This variable is computed by the program if FORS, FOCI, or SOCI is chosen, otherwise it must be entered.
Note: there is a known bug (with no known fix) when using IEXCIT with MULT greater than 1. The program generates extra CSFs, with excitations higher than that given here. The same thing happens with singly occupied AOS and BOS MOs.
An input such as
$drt iexcit=2 ndoc=a nalp=b nval=c next=0 $end
actually generates the same set of CSFs as
$drt soci=.t. ndoc=a nalp=b nval=0 next=c $end
rather than what you'd expect it to.

* * the next variables define the single reference * *

The single configuration reference is defined by filling in the orbitals by each type, in the order shown. The default for each type is 0.

Core orbitals, which are always doubly occupied:

NMCC
= number of MCSCF core MOs (in $DRT only).
NFZC
= number of CI frozen core MOs (in $CIDRT only).

Internal orbitals, which are partially occupied:

NDOC
= number of doubly occupied MOs in the reference.
NAOS
= number of alpha occupied MOs in the reference, which are singlet coupled with a corresponding number of NBOS orbitals.
NBOS
= number of beta spin singly occupied MOs.
NALP
= number of alpha spin singly occupied MOs in the reference, which are coupled high spin.
NVAL
= number of empty MOs in the reference.

External orbitals, occupied only in FOCI or SOCI:

NEXT
= number of external MOs. If given as -1, this will be set to all remaining orbitals (apart from any frozen virtual orbitals).
NFZV
= number of frozen virtual MOs, never occupied.

* * * the final choices are seldom used * * *

INTACT
= flag to select the interacting space option. The CI will include only those spin couplings which have a nonvanishing matrix element with the reference configuration.

MXNINT
= Buffer size for sorted integrals. (default=20000)

MXNEME
= Buffer size for energy matrix. (default=10000)

NPRT
= Configuration printout control switch. This can consume a HUMUNGUS amount of paper!

0 = no print (default)

1 = print electron occupancies, one per line.

2 = print determinants in each CSF.


Back to list of input groups...