Generalized symmetry-adapted interpolation procedure for finding transition states in internal rotations

Abstract

A constrained procedure is examined for internal rotations and generalized in terms of the symmetry of the system, initial conditions, and intuitive ideas such as Hammond's postulate and the Brønsted coefficient. We find that this symmetry‐adapted interpolation procedure can be used to describe potential energy surfaces with a discrepancy from point‐by‐point calculations much smaller than the currently used procedures. New relations in terms of a reduced number of independent calculations are given from which second derivatives are obtained. Terms representing the Brønsted condition are shown to appear naturally in the potential energy expression, showing the simplicity of the method as well as giving a more quantitative interpretation of the Hammond postulate. Surfaces are calculated for the internal rotation of the ethylene–sulfur dioxide complex, ethane, stilbene and the CO2HCN tetramer internal motion. The model requires only two input values at each minima (or initial and final structures), representing a substantial reduction in computational cost and has been able to predict the location of the transition state with very small error. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 563–576, 1999