Subject: DFT single point calculations

From: James Pugh <[email-masked]>
Date: Wed, 14 Aug 1996 13:00:03 -0700 (PDT)

CCL:

I have been working on a carbene rearrangement scheme and have, after 
much effort, been able to complete all of the calculations at the 
RHF/6-31G** level.  These calculations include both ground and transition 
state structures.  Each of these has been characterized by a frequency 
calculation and found to be a valid point on the potential energy 
surface.  The next step is to do single point calculations using a 
post-HF or correlated method.  This is where I have encountered much 
difficulty.

I have attempted MP2, MP3, MP4, MP2(full), QCIS, QCISD, and QCISDT 
methods, but each has either failed or was beyond the scope of the 
computer resources at my disposal.  By failure I mean that the energy 
values of some of the transition states was below that of the starting 
material.  My question is thus:

I have recently been doing Density Functional Theory single point 
calculations on the optimized geometries at the RHF/6-31G** level.  Is 
this a valid approach to the problem?  In doing a literature search, I 
have never seen this used before.  Researchers have either used entirely 
ab-initio calculations or DFT - not a mixture of both.  Since the DFT 
single point calculations are working out nicely, I would very much like 
to continue.  

Thank you very much for any help you might offer.

Jim Pugh
Department of Chemistry
Oregon State University
e-mail: [email-masked]