Subject: Re: CCL:PM3tm-summary-later comment

From: kim <[email-masked]>
Date: Wed, 12 May 1999 12:37:11 -0700 (PDT)

dear piotr,

after reading your pm3(tm) commentary, it left me wondering about the pm3(tm) in 
general.  looking further into cro3 problem, and comparing the hyperchem and 
spartan implementations (using molecules with the same symmetry, geom. 
optimized) on a pc i had the following results:

                     spartan              hyperchem

bond lengths:          1.63                 1.63
heat of formation   -79.14 kcal/mol      -185.44 kcal/mol
total energy        -1132.304 ev          -1132.369  ev

so while the heats of formation are vastly different, the electronics portions 
of both programs would seem to yield very similar results.  however, it would 
seem the energetic points of reference for computing the heats of formation for 
the two programs are very different (anybody have some comment on these 
discrepancies?) regarding the h-h repulsion, since there aren't hydrogens 
involved...that shouldn't be the difference.  i checked with spartan using the 
hhon and hhoff keywords, and there was no difference there. the end of your 
message sounded like pm3(tm) might become a hopeless morass, but now the problem 
seems rather localized.  it would be nice if this discrepancy could be resolved, 
but, it would require some detailed information from wavefunction.  the last 
time i checked, the publication regarding the details of the pm3(tm) development 
has not hit print.

excerpted:

> The difference between implementations in the above-mentioned programs was
> pointed out: in Spartan correction for H-H repulsion is added by default in
> calculations containing tms. (Unfrotunately I couldn't check if this was my
> problem since the keyword turning it off does not work in PC Spartan Pro).
> 
> Finally, thanks to Alan Shusterman, we were able to compare data for CrO3.
> C3v geometry gave in all versions of Spartan (unix, mac, pc) heat of
> formation of -79.14 kcal/mol while Hyperchem yielded -185.5 kcal/mol
> (experimental data: about -52 kcal/mol JPC 1996, 100, 6354) - geometrical
> results are the same from both programs.
> 
 
 last note: the author has no connection with either hypercube or wavefunction.

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=     Kim F. Ferris                            =
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