Subject: Re: CCL:`Long range Coulomb forces in PM3 semiempirical methods?

From: elewars <elewars|at|trentu.ca>
Date: Fri, 18 Jul 2003 12:00:04 -0400

2003 July 18

Hello,

If by long range coulombic forces you mean van der Waals forces, SE methods
probably can't be relied on, although in particular cases they may give (happen to
give) reasonable results. See:

C. J. Cramer, _Essentials of Computational Chemistry_, Wiley, 2002, p 139: "For
intermolecular interactions that are weak in nature, e.g. those arising from
London forces (dispersion) or hydrogen bonding, semiempirical methods are in
general unreliable."

Standard SE methods don't really "include" van der Waals forces, because they were
parameterized with an eye on heats of formation, geometries, ionization
potentials, and dipole moments.

E. Lewars
===========

Connie Chang wrote:

> Hi --
>
> I was wondering if anyone out there knew if the PM3 semiempirical method
> includes long range Coloumbic forces?
>
> Thanks!
> Connie Chang
>
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