Empirical valence-bond models for reactive potential energy surfaces using distributed Gaussians

A new method for constructing empirical valence bond potential energy surfaces for reactions is presented. Building on the generalized Gaussian approach of Chang-Miller, V-12(2)(q) is represented by a Gaussian times a polynomial at the transition state and generalized to handle any number of data points on the potential energy surface. The method is applied to two model surfaces and the HCN isomerization reaction. The applications demonstrate that the present method overcomes the divergence problems encountered in some other approaches. The use of Cartesian versus internal or redundant internal coordinates is discussed.