$GCILST group      (required by MCSCF if CISTEP=GENCI)
                                (required if CITYP=GENCI)
 
    This group defines space products to be used in the
general CI calculation, or in a MCSCF wavefunction.  The
input is free format.
 
Line 1: NSPACE ISYM
 
The first line gives the total number of space products to
be entered in the second lines.  The option ISYM can be
omitted, or given as 0, in which case the program will
verify that all space products typed in the second lines
indeed have the spatial symmetry defined by STSYM in the
$GEN or $CIGEN input groups.  If ISYM is 1, the user is
indicating that more than one space symmetry is known to be
in the list, that this is intentional, and the program
should proceed with the calculation.  This might be of use
in state averaging two representations in a group that has
more than two total representations, and therefore faster
than turning symmetry off completely by GROUP=C1.  ISYM=2
has the same meaning but turns on additional printing.
 
Line 2 is repeated NSPACE times.  Each line 2 contains NACT
integers, which must be 0, 1, or 2, and therefore tells the
occupation of each of the active orbitals in each space
product.  An example input is:
 $GEN     GLIST=INPUT NELS=6 NACT=4 SZ=0.0 $END
 $GCILST
5
2 2 2 0
2 1 2 1
2 0 2 2
2 2 0 2
0 2 2 2
 $END
which generates 6 Ms=0 determinants, much less than the 16
determinants in a C1 symmetry full list for 6 e- in 4 MOs.
 
The second space product above generates two determinants.
All space products with singly occupied orbitals are used
to form all possible determinants, to ensure that the final
states are eigenfunctions of the S**2 operator (meaning
they will be pure spin states).
 
Note that there is no way at present to generate lists such
as singles and doubles from a single reference.
 
Convergence of MCSCF calculations with arbitrary lists of
space products will depend on how well chosen your list is,
and may very well require the use of FULLNR or JACOBI
convergers.
 
A utility program to pre-select the important part of CI
expansions with high excitation levels, based on
information from CI-SDT calculations, is distributed with
the source code.  See the file
       ~/gamess/tools/ci-tools/select/readme.1st
for more information.
 
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