Subject: CCL: NDDO semiempirical parameters

From: "Mark Thompson" <mark~at~planaria-software.com>
Date: Fri, 13 Jun 2003 13:38:44 -0700

> I have a couple of questions about semiempirical parameters in
> NDDO methods (MNDO, AM1...):
>
> 1) Do you have any routine or the iterative formulas to obtain
> the derived parameters, rho1 and rho2, from the optimized ones
> (namely 1 center 2 electron integrals, g_ij, and zeta_i) ??

Other than the discussion given in the original Thiel and Dewar papers, you
pretty much have to write your own; its not too hard.  (If you do find other
sources on this, please summarize to the CCL).

> 2) Can you suggest any references which explicitly comment on the
> individual influence of the NDDO parameters upon calculated
> molecular properties?
>   E.g.: If one varies the resonance integrals (beta_i), what is
> the effect upon geometries? Or if one varies the one center one
> electron integrals (U_ii), what is the effect upon charge distribution?

The two original Jimmy Stewart PM3 references would be a good place to start
(also email Jimmy himself).  The references are :
J.Comp.Chem 10, 209-220 (1989)
J.Comp.Chem 10, 221-264 (1989)

You can experiment with some of these param modifications, by hand, using
ArgusLab.  Simply modify the AM1, PM3, MNDO params (in am1.prm, pm3.prm, and
mndo.prm) with a text editor and see what happens.  Make sure you save
copies of the original parameter files.  Download it at
http://www.arguslab.com

Cheers,
Mark

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Mark Thompson, Ph.D.
Planaria Software
PO Box 55207
Seattle, WA  98155
FAX: 206-440-3305

ArgusLab is available at:
http://www.arguslab.com
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