COMBINED AB-INITIO EMPIRICAL-APPROACH FOR OPTIMIZATION OF LENNARD-JONES PARAMETERS

Obtaining accurate Lennard-Jones (L-J) parameters is a vital part of t he optimization of empirical force fields due to their significant con tribution to condensed-phase properties. We present a novel approach t o optimize L-J parameters via the use of ab initio data on interaction s between rare gas atoms and model compounds combined with the reprodu ction of experimental pure solvent properties. Relative values of ab i nitio minimum interaction energies and geometries between helium or ne on and model compounds were used to optimize the relative magnitude of the L-T parameters. Absolute values of the L-J parameters were determ ined by reproducing experimental heats of vaporization and molecular v olumes for pure solvents. Application of the approach was performed on methane ethane, and propane. Free energies of aqueous solvation and b utane pure solvent and aqueous solvation calculations were used to tes t the developed L-J parameters. The new alkane parameters are similar or improved as compared with current empirical force field parameters with respect to experimental pure solvent properties and free energies of aqueous solvation. Also included is a description of the internal portion of the force field. (C) 1998 John Wiley & Sons, Inc.