Subject: Re: CCL:PM3 AND AM1 FOR H BONDS

From: Csonka Gabor <[email-masked]>
Date: Wed, 09 Apr 1997 09:30:54 +0200

E. Lewars wrote:

  1997  April 8

   There was a recent question about AM1 vs. PM3 for studying hydrogen
  bonds.

   Dr J. J. P. Stewart, the inventor of PM3, tells me that he can't
  find a
  specific ref to this, but Shields has published on the superiority
  of PM3
  in the last 3 years or so.  Some other refs to PM3 cf. AM1 (I don't
  know
  offhand if any of these are on H bonding):

    If you try to optimize the water dimer with PM3, you get the right
  geom.; if
  you use AM1 you get the wrong one.  See too "Experiments in
  Computational
  Organic Chemistry", by Hehre, Burke, Shusterman and Pietro
  (Wavefunction, 1993),
  p. 43, where PM3 is recommended for H-bonded molecules because, it
  is said, it
  works better than AM1.

  E. Lewars  Chem Dept Trent U, Peterborough  Ontario  Canada

I noticed Dr J. J. P. Stewart via E-mail about the problems with PM3,
and we are publishing a paper on this problem. The paper was accepted
for THEOCHEM and I'll present the problem on the next ICQC too.

In short: the equilibrium geometry is sometimes good, but the
hypersurface is wrong. The error is in the oscillating nature of the
Gaussian correction functions of the CRF in PM3. This is why the PM3
fails seriously for sugars, c.f. G.I. Csonka, K. Elias, I.G. Csizmadia,
J. Comp. Chem., 18 (1997) 330-342 and references therein.

See more details and references in:

http://web.inc.bme.hu/~csonka/crf/crf.htm

 Gabor I. Csonka    e-mail: [email-masked]
 Lab.Chimie Theorique      Universite Henri Poincare
 B.P. 239                  54506 Vandoeuvre-les-Nancy FRANCE
 tel: +33-3.83.91.25.29    fax: +33-3.83.91.25.30
 http://www.ch.bme.hu/inc/csg.html