

An alternative would be to use MOLCAS and to do a CASSCF calculation with
subsequent CASPT2. Up to 14 active electrons in 14 orbitals is possible
with MOLCAS. The accuracy is within 0.2 eV, given that a reasonable
choice of the active orbitals for the states of interest is made, and
a reasonable basis set is used. Remember, the s-tetrazine calculations
were done with MOLCAS on the C4 cluster.
(Schuetz, Hutter, Luethi, JCP 103, 7048 (1995).
One problem you may have is, that the codes are not integral direct.
So you have to store the ERIs on disk, which may kill you, if your
molecule is too large. In LUND we have a multifile I/O system in experimental
status, which allows to go beyond the 2 GByte limit, imposed by AIX on the
RS6K. Furthermore, distributed parallel, integral-direct implementations
of CASSCF/CASPT2 are under development, but these won't be available until
next year.

Martin

-- 
Martin Schuetz, Ph.D.                       Phone: +46 46 222 45 01
Dep. of Theoretical Chemistry               FAX:   +46 46 222 45 43
University of Lund
SWEDEN
E-mail: [email-masked], [email-masked]

-----cut here-----