Subject: Question about Electrostatics in Molecular Mechanics

From: BILL WELSH <[email-masked]>
Date: Thu, 03 Aug 1995 16:34:34 -0500 (CDT)

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