Subject: Re: Compatability of Ab Initio results

From: [email-masked] (Theresa Windus)
Date: Wed, 8 Dec 93 15:02:03 CST

Dear netters:

  In reply to:
>From: Szilagyi Robert <[email-masked]>
>Dear Andy,
>
>	I tested the g92 and the GAMESS packages on
>tungsten carbene complexes, using ECPs.
>
>	The GAMESS with SBK ECP is much better than
>the G92 LANL1MB or LANL1DZ. Now I am going to test
>the origin of the differences. They are due to the basis
>set or the software. I will summarize the results on net
>and to you of course.
>
>Cheers,
>
>			Rob

   I am sure Rob will find that the major difference is the basis set.
We have run many tests and the general conclusion is that GAMESS and
GAUSSIAN give the same energy (out to the seventh decimal place) IF
the same basis set, number of d's (6 or 5), geometry and wavefunction
are used.  Occasionally, different energies will result from different
initial guesses.  These are generally cases where the initial guess 
creates a wavefunction of the "wrong" symmetry (i.e. not the ground
state symmetry).  Either program will occasionally come up with the
"wrong" initial guess.
   Since GAMESS and GAUSSIAN use different optimization routines,
different geometries CAN be found.  Usually, however, for the same
initial geometry and same initial hessian the same final geometry is
found (within chemical accuracy).  I am probably biased, but I have
generally found that transition states are easier to find in GAMESS.  I
have had a couple of occasions where I couldn't find a transition state
with GAUSSIAN (given a "not too bad" starting geometry) that GAMESS
found in about 10-15 steps.  Optimization or transition state searches
are "tricky" things and the algorithm used can occasionally do different
things.
   Hope this helps!

Theresa Windus
Department of Chemistry
Iowa State University
Ames, IA  50011

e-mail: [email-masked]