Subject: PM3 AND AM1 FOR H BONDS

From: "E. Lewars" <[email-masked]>
Date: Tue, 8 Apr 1997 12:30:06 -0400 (EDT)

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):

1)  Extensive comparison: J Computer-Aided Molecular Design, 4 (1990) Issue 1
    (Special issue) ; discusses PM3, AM1 and MNDO
2)  W. Thiel, Tetrahedron, 44 (1988) 7393
3)  J. J. P. Stewart, J Comp Chem 11 (1990) 543
                                  10 (1989) 209
                                  10 (1989) 221
                                  12 (1991) 320
4)  Dewar et al J Comp Chem 11 (1990) 541
5)  Smith et al J Comp Chem 13 (1992) 640
6)  In a letter to the Net (1995), Andy Holder (SemiChem) said:
    PM3 is better than AM1 for NO2 compounds and usually a little better
    for geom's.  It is not as good for MO's and is unreliable for charges.
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  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
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