An empirical valence bond model for constructing global potential energy surfaces for chemical reactions of polyatomic molecular systems

Abstract

An empirical valence bond (EVB) model is proposed for constructing reactive potential energy surfaces of polyatomic molecular systems. Specifically, it is shown how the exchange potential V{sub 12}(q) of the EVB model can be chosen so that the EVB potential V(q) {triple bond} 1/2(V{sub 11}(q) + V{sub 22}(q)) - ((1/2(V{sub 11}(q) - V{sub 22}(q))){sup 2} + V{sub 12}(q){sub 2}){sup 1/2} exactly reproduces the transition-state geometry, energy, and force constant matrix obtained by an independent ab initio calculation. (Here q denotes all the 3N-6 nuclear coordinates of the N-atom system, and V{sub 11} and V{sub 22} are empirical diabatic, i.e., nonreactive, potential functions that describe the reactant and product regions of the potential surface, respectively.) Application of the overall prescription to a variety of two-dimensional test potential surfaces shows that this version of the EVB model provides an excellent description of reactive potential surfaces for a wide variety of situations.