Using force fields methods for locating transition structures

Abstract

A previously proposed strategy of using force field methods for generating approximations to the geometry of transition structures is extended to also estimating an approximate Hessian matrix. These two components allow an automated method for locating first order saddle points, which is an essential requisite for studying chemical reactions of systems with many degrees of freedom. The efficiency of using an approximate force field Hessian matrix for initiating the geometry optimization is compared with the use of an exact Hessian. The force field Hessian in general requires more geometry steps to converge, but the additional computational cost is offset by the savings from not calculating the exact Hessian at the initial geometry.