From:	tony (- at -) bioc1.biosym.com (Tony Schmidt)
Date:	Fri, 4 Aug 95 08:57:38 -0400
Subject:	Re: CCL:Question about Electrostatics in Molecular Mechanics

On Aug.8 Bill Welsh wrote:

Dear Netters,

Please help settle a small controversy.  For a particular molecular
mechanics calculation, I derived partial atomic charges from bond
dipole moment measurements made in nonpolar solvent.  I then ran
molecular mechanics calculations using an in vacuo dielectric constant
of 1.00.  A colleague argues that I must use a dielectric constant
appropriate to the nonpolar solvent from which the charges were
derived (e.g., 2-3).  It seems to me that the charges already embody
the effect of the nonpolar solvent's dielectric constant, and so using
the in vacuo value of 1.00 is okay and perhaps preferred.  Stated another
way, it seems to me that using these charges AND the dielectric of 2-3
would count the effect of the nonpolar solvent twice.

Any opinions on this matter are appreciated.

Thanks ...

Bill Welsh
Dept. of Chemistry
Univ. of Missouri-St. Louis
-----------------------------------------------------

If you have dipole moments in solvent, you may have to scale them for vacuum
using e.g. strategy by Sharp et al, J.Phys.Chem. 96, 3822 (1992).

Tony Schmidt
tony -x- at -x- biosym.com


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