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$ORMAS group (required by MCSCF if CISTEP=ORMAS)
(required for CITYP=ORMAS)
This group partitions an active space, defined in $DET
or $CIDET, into Occupation Restricted Multiple Active
Spaces (ORMAS). All possible determinants satisfying the
occupation restrictions (and of course the space symmetry
restriction given in $DET/$CIDET) will be generated. This
group's usefulness lies in reducing the large number of
determinants present in full CI calculations with large
active spaces.
There are no sensible defaults for these inputs, but if
the group is entirely omitted, a full CI calculation will
be performed. That is, the defaults are
NSPACE=1, MSTART(1)=NCORE+1, MINE(1)=NELS, MAXE(1)=NELS
meaning all active orbitals are in one partition.
NSPACE = number of orbital groups you wish to partition
the active space (NACT in $DET/$CIDET) into.
MSTART = an array of NSPACE integers. These specify where
each orbital group starts in the full list. You
must not overlook the NCORE core orbitals in
computing MSTART values. Space I runs from
orbital MSTART(I) up to orbital MSTART(I+1)-1,
or NACT+NCORE if I is the last space, I=NSPACE.
IMPORTANT !!!! Remember to make sure your orbitals have
been reordered to suit MSTART, using NORDER in $GUESS.
MINE = an array of NSPACE integers. These specify the
minimum numbers of electrons that must always
occupy the orbital groups. In other words,
MINE(I) is the minimum number of electrons that
can occupy space I in any of the determinants.
MAXE = an array of NSPACE integers. These specify the
maximum numbers of electrons that must always
occupy the orbital groups. In other words,
MAXE(I) is the maximum number of electrons that
can occupy space I in any of the determinants.
The number of active electrons is NELS in $DET or $CIDET,
and the program will check that MINE/MAXE values are
consistent with this total number.
Input for Coupled Electron Pair Approximations
These two keywords provide size-extensivity corrections for
singly and doubly excited CI calculations. At present,
these approximate corrections may only be applied to a
single state. The CISD may follow RHF (single reference,
SR) or complete active space (multireference, MR)
calculations. Usually, the final ORMAS orbital space will
be the entire external space of the SR-CISD or MR-CISD
calculations. The excitation level (MAXE) into this space
should only be two. The number of electrons being
correlated (NELS in $CIDET) is denoted Ne. The value of a
parameter G determines the weight of the approximate size-
extensivity correction, with the literature containing
several possible choices: GVAL here sometimes is written
as -(1-G) in the literature. The first order density
matrix for the chosen CEPA-style correction will be
generated, and used for property calculation.
CEPA = NONE ordinary SR-CISD or MR-CISD (default)
= CEPA0 Coupled Electron Pair Approximation,
whose GVAL= 1.0
= ACPF Averaged Coupled Pair Functional,
whose GVAL= (Ne-2)/Ne
= AQCC Averaged Quadratic Coupled-Cluster,
whose GVAL= (Ne-3)(Ne-2)/[Ne(Ne-1)]
= READ user will supply the desired GVAL.
GVAL = is given only when CEPA=READ
An example of the SR-AQCC size-extensivity correction for a
molecule with 10 chemical cores, 8 occupied valence
orbitals, and 163 total MOs is
$CONTRL SCFTYP=RHF CITYP=ORMAS RUNTYP=ENERGY
$CIDET NCORE=10 NACT=153 NELS=16
$ORMAS CEPA=AQCC NSPACE=2
MSPACE(1)=11,19 MINE(1)=14,0 MAXE(1)=16,2
A MR-CEPA case with N active electrons and M electrons in
filled valence orbitals should use three spaces, with NELS
M+N; MINE M-2,N-2,0; and MAXE M,N+2,2.
Review: P.G.Szalay, in Modern Ideas in Coupled-Cluster
methods, R.J.Bartlett (ed), World Scientific, Singapore
(1997), pp 81-123.
* * * * *
BLOCK = a flag to request that natural orbital generation
for CISTEP=ORMAS MCSCF or CITYP=ORMAS CI runs
should prevent mixing between the NSPACE orbital
subspaces. This means the NOs only diagonalize
the diagonal blocks of the density, and are thus
not the genuine NOs. However, these approximate
NOs can be used with MOREAD to exactly reproduce
the ORMAS energy, which is invariang to rotations
within the orbital subspaces. (Default=.FALSE.)
QCORR = a flag to request Davidson-style +Q corrections.
If this is not sensible for your CI choice, the
program will not print this correction, anyway.
The default is .TRUE.
FDIRCT = a flag to choose storage in memory of some
intermediates. This is very large, and slower in
the case of many occupied orbitals, but helpful
with a smaller number of orbitals. Therefore the
default for this is .TRUE. for MCSCF runs, but
.FALSE. during CI computations.
*** See REFS.DOC for more information on using ORMAS ***
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generated on 7/7/2017