Modeling chemical reactions for conformationally mobile systems with force field methods

Abstract

A previously proposed method for modeling transition structures as minima on the seam of two force field energy functions, denoted SEAM, is analyzed with respect to improvements in the functional form of key energetic terms and parameters. It is shown that the SEAM method is capable of accurately reproducing transition structures from electronic structure methods, at a fraction of the cost. The SEAM method can be used to automatically sample different conformational transition structures for a given reaction. Depending on the underlying force field and the reaction, the relative energies of the transition structures may or may not be sufficiently accurate for selecting the important low-energy structures. A combination of using the SEAM method for determining geometries and a low-cost electronic structure method for single point energy calculations appears to be an attractive combination for identifying low-energy transition structures for systems having many degrees of freedom.