Subject: Spin Contamination in Correlated Optimizations

From: "Michael D. Bartberger" <[email-masked]>
Date: Sun, 24 Sep 1995 11:54:25 -0400 (EDT)

Hello all:

A while back I posted a question regarding regarding spin-projected 
energies vs. non-, and UHF vs. ROHF in doing optimizations on systems 
where spin contamination is relatively high.   I summarized these 
responses and the interested reader can find these in the archives.

Let me extend this one step further......   it was mentioned that UMPn 
optimizations using a spin-contaminated reference can lead to terrible 
geometries......   I have also seen this comment given in various texts 
and papers, although no examples are given.  I would like to hear from 
readers who have experienced this for themselves.   Any references, 
pointers, or "personal accounts" would be appreciated.

We do computational studies on fluorinated radicals, and spin 
contamination in the UHF wavefunction is often quite high.  I have usually
stayed with UHF geometries, even on systems small enough where MPn
optimizations might be feasible.   I'd like to collect some more ammunition
on this subject.

Thanks!!!

Regards,

Michael 
________________________________________________________________________________

 Michael D. Bartberger         [email-masked]        TEL: (904) 392-3580
 Department of Chemistry       [email-masked]         FAX: (904) 846-0296
 University of Florida
 Gainesville, FL  32611
 USA
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