Subject: Gaussian 90/92 calculations

From: [email-masked]
Date: Fri, 20 Nov 92 20:21:30 EST

To anyone who can help me:  I have been running Gaussian calculations on
some catechols and related molecules.  I am interested in calculating their
electronic transition moments, i.e., the change in charge distribution which
occurs when an electron is excited from the HOMO to the LUMO.  To do this,
one sums the squares of the AO coefficients in a special way.  Since the AO's
and MO's are supposed to be normalized, I thought I would check by summing the
squares of the AO coefficients in each MO.  The first half dozen or so were
close to 1.  Then they went way down (about .4 and lower).  The HOMO summed
to about .6, the LUMO to 1.4, and the four or five above that went way up --
1.4, 3.5, 6.0, 4.2, 8.2, etc.  Some get REALLY big after that (20.0!).
 
     Anyway, I was wondering not only what might cause this, but how one can
fix the problem.  Does this happen under special conditions in Gaussian?  Is
there a way to adjust for it, either in the Gaussian runs or after the fact?
 
     Any insight into how to get around or fix this problem would be most
welcome.  Thanks!
 
                                           Louis Grace
                                           Department of Chemistry
                                           The University of Michigan