Subject: CCL: CASSCF and degenerate state

From: Wai-To Chan <[email-masked]>
Date: Wed, 27 Jun 2001 22:17:27 -0400 (EDT)

<<<<<<<<<<<<<<<<<
Dear CCL!

I have problems performing a CASSCF calculation on an open shell 
pi-system with a doubly degenerate ground state (using Gaussian98).

Any help?

Thanks, Jens >--<

  Appended to this message
is a g98 multi-step input file for a CASSCF calculation of the open-shell
singlet of molecular oxygen. It gives an optimized bond distance of 
1.2072 angstrom in close agreement with the value  
quoted in a previous g98-casscf study from
IJQC, vol 65, pg 787-801 (1997). Note that the second part of this job
is just to show you the natural orbitals used in the subsequent 
CASSCF step. Hope this is pertinent to your study.  

Wai-To Chan 

*************************************
%chk=o2oss-cas
%mem=64MB
# uhf/6-311G* guess=mix

O2 biradical singlet symmetry-broken UHF solution 

0 1
O
O 1 roo

roo 1.20

--Link1--
%chk=o2oss-cas
# uhf/6-311G* geom=check guess=read symm=noscf pop=(regular,no)

O2 biradical singlet natural orbitals 

0 1

--Link1--
%chk=o2oss-cas
%mem=64MB
# cas(2,4,qc)/6-311G* geom=check guess=read nosymm opt

O2 biradical singlet CASSCF. 2 SOMO electrons 4 Active MOs

0 1

*******************************************