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 # - at - # biosym.com