Subject: MM/QM Calcns

From: [email-masked] (Neil S. Ostlund)
Date: Thu, 15 Sep 1994 12:39:58 -0400

Mark Thompson recently replied to a request for info about mixed
MM/QM methods.

>		 To my knowledge, Argus is the only code designed from
>	     its inception to be able to describe chemical systems
>	     with multi-Hamiltonian methods (as opposed to merging
>	     pre-existing mature codes, often with highly dissimilar
>	     data models).  It's been very easy (for me) to modify
>	     and extend the code when we have new ideas to try out.

Mark forgot to mention HyperChem which from its inception has solved
the problem of defining the boundary problem between a QM region
and a Mol Mech region and allowed a quantum calculation to include the
electrostatic effects of the MM region.  We have never managed to get
around to publishng the method but the manuals describe it thoroughly.

I feel that we do a better job than most so that, for example, methyl
amine (MM-CH3, QM-NH2) doesnt just give a wave function that looks like
that for NH3 but the charge distribution actually looks like that for 
methyl amine.  We dont cap the quantum region with a Hydrogen atom but
with an "effective atom" that simulates the MM region.

Cheers.