From jan@si.fi.ameslab.gov  Thu Nov  5 04:35:02 1992
From: jan@si.fi.ameslab.gov (Jan Jensen)
Subject: Semiempirical vs. Molecular Mechanisms Models
To: chemistry@ccl.net
Date: Thu, 5 Nov 92 10:35:02 CST


   Tom Slee raised a very interesting point: semiempirical theory is not 
necessarily better at conformational analysis than molecular mechanics (MM).
The two references are very informative (I admit I know very little about
MM), and seem to indicate that MM2 is the program of choice.  Have similar
studies been done with CHARMM?  
   One problem I have with MM, however, is the strong dependence on 
parameters - semiempirical methods retain some quantum mechanics to (in 
principle) model chemistry that parameters have not covered explicitly.
Is it perhaps possible that semiempirical methods would be better for
systems for which MM has not been specifically parameterized, and for
which no (or little) experimental data exist to check against?  I want
to emphasize that I'm not trying defend any method, I'm simply trying
to learn.

				Jan Jensen

P.S. I think I inadvertently send an air-mail to the list.  My apologies.