Subject: configuration interaction in semiemp. schemes?

From: <[email-masked]>
Date: Tue, 10 Oct 1995 14:35:11 CET

Dear all,

I have what I think is a simple (minded) question:

As far as my limited knowledge goes, it is generally true that in ab initio
schemes, calculated heats of formation get 'better' as more electron
correlation is taken into account -- either through configuration interaction,
use of Moeller-Plesset schemes or other technique. What I'd like to know is:
how does this apply to semi-empirical schemes?

My personal 'feeling' is that, since SE schemes were parameterized to closely
reproduce experimental heats of formation (for a limited set of training 
compounds) in the single determinant form, any correlation scheme lowering this
energy will lead to larger (average) deviations from experimental values -- if
this is true, one would have to use the HoF from a single determinant
calculation, while certain other characteristics might be better calculated
using CI schemes (thinking of UV spectra in particular). Is this correct?

==========One man's FF@ state-of-mind is another man's Hydropsyche!===========
| Henk Verhaar                        |  e-mail:  [email-masked] |
| Research Institute of Toxicology    |                                      |
| Environmental Toxicology Section    |  phone:   +31 30 535338              |
| Utrecht University, the Netherlands |  fax:     +31 30 535077              |
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