Subject: Convergence of CASSCF calculations

From: [email-masked] (Charles Martin)
Date: Tue, 7 Mar 1995 01:29:56 -0600 (CST)

Netters,
	Recently one of the grad students in our group has been using
Gaussian CASSCF calculations to describe the excited state potential
energy surface of a long chain polyene:

	C=C-C=C-C=C-C=C-C=NH2(+)   (the polyene is twisted and has no symmetry)

	He has been unable, however, to converge the CASSCF(2nd root)
calculations at some of the twisted geometries.

	Of course, there could be a near degeneracy which is causing
the problem, but I am also suspecting that CASSCF orbitals which Gaussian
uses may be inappropriate, and that instead the virtual orbitals for the
CASSCF active space calculation should be some Unitary Transformation
of the HF orbitals which Gaussian uses (like Improved Virtual Orbitals).

	First, I am wondering if anyone else has had similar experiences
and could offer some insight or suggestions.

	Second, I would like to know if anyone has a proogram which will
perform such Unitary Transformations with Gaussian, or will I have to
write my own or use a different package.

	Third, just out of curiosity, do any other packages perform 
such feats with ease?  For instance, I have programs which will do this 
using the COLUMBUS suite of codes, but the COLUMBUS codes and my adjoining 
codes are pretty  low compared to Gaussian.  On the other hand, COLUMBUS
is pretty easy to interface to, although I do not know alot about the
internal components of the other packages available.  Perhaps we could
open up a discussion about this.  For instance, are there mail lists
for users and programmers of specific packages (GAMESS, COLUMBUS, GAUSSIAN,
 etc.)

	With Best Regards

	Charles Martin
	Theoretical Biophysics
	The Beckman Institute
	The University of Illinois at Urbana-Champaign
	([email-masked])