ANALYTICAL ENERGY DERIVATIVES FOR A REALISTIC CONTINUUM MODEL OF SOLVATION - APPLICATION TO THE ANALYSIS OF SOLVENT EFFECTS ON REACTION PATHS

Analytical expressions for the first and second derivatives of the Har tree-Fock energy have been derived in case of a solvated system simula ted by a multipolar charge distribution embedded in a cavity of arbitr ary shape and a solvent represented by a dielectric continuum. A compu ter code has been written on these bases. It allows geometry optimizat ions and more generally the determination of the critical points of th e potential energy surface for a molecular system interacting with a s olvent as easily as in the case of an isolated molecule. The use of th is code is illustrated by the computation of the main features of the reaction path of a Menshutkin-type reaction in various solvents. The r esults compare pretty well with those obtained by a full Monte Carlo s imulation of the solvent by Gao, This agreement supports the idea that solvents, including water, can be safely modeled by a continuum. The advantage of such models rests in the fact that they allow refined com putations on the solute at a minimum computational expense. (C) 1996 A merican Institute of Physics.