From jstewart |-at-| fai.fai.com  Wed Sep  9 14:69:21 1992
Date: Thu, 10 Sep 92 08:04:21-1795
From: Dr. James Stewart <jstewart -8 at 8- fai.com>
To: chemistry&$at$&ccl.net
Subject: Some Semiempirical Thoughts


  Some Semiempirical Thoughts

1.  As Joe Leonard correctly suggested, I am not an employeee
of Fujitsu.  Stewart Computational Chemistry is a private
consulting concern.  Fujitsu is a customer.

2.  I regret my observation on SAM-1.  However, let me explain.
The results I reported for SAM-1 were taken from an official
publication written by Prof Dewar, and approved for public
release.  

3.  Drs Caoxian Jie and Jianguo Yu expressed interest over the
Gaussians in AM1.  The history of these terms is as follows:
In 1982 Prof Dewar asked me to work on correcting the known
error in MNDO, specifically to correct for the excessive 
repulsions at roughly the van der Waals' distances.  After a
short time, it became clear that the fault could be corrected
using the method of operator equivalents: a modification to
the core-core terms could mimic the true correction, which should
more correctly have been made elsewhere.

A Gaussian series is like a Fourier series: you can model any 
function you want with it.  For that reason, I chose to add 
Gaussians to the core-core terms.  This was intended as an 
interim measure; at least, that was my thought at that time.  
Hopefully, we can soon do away with operator equivalents, 
which really only treat the symptom and not the cause.

4.  MOPAC-7 will be coming out in a few months.  Details are
still not finalized, but should be in about a month.  At the
present time, however, it looks likely that MOPAC-7 will
have the following features:

 e.  Most important, the amount of high-quality code contributed
by various people is at an alltime high.

 d.  Some symmetry has been added.

 b.  One, two, and three dimensional systems will be supported.

 c.  Electronic band-structures will be calculable.

 f.  In one form, MOPAC-7 will be placed in the public domain.

 g.  The Manual has been expanded.  This is in response to so
many requests for more detail.

 a.  Copies of the program and the manual will be available from 
     several sources, including QCPE.


None of this is definite, of course.  For just now, MOPAC-7 should
be regarded as `vaporware'.  

James J. P. Stewart

Tel 719 488 9416
FAX 719 488 9758
E-mail jstewart;at;fai.com