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

A constrained procedure is examined for internal rotations and generalized in terms of the symmetry of the system, initial conditions, and intuitive i deas such as Hammond's postulate and the Bronsted coefficient. We find that this symmetry-adapted interpolation procedure can be used to describe pote ntial energy surfaces with a discrepancy from point-by-point calculations m uch smaller than the currently used procedures. New relations in terms of a reduced number of independent calculations are given from which second der ivatives are obtained. Terms representing the Bronsted condition are shown to appear naturally in the potential energy expression, showing the simplic ity of the method as well as giving a more quantitative interpretation of t he Hammond postulate. Surfaces are calculated for the internal rotation of the ethylene-sulfur dioxide complex, ethane, stilbene and the CO2-HCN tetra mer internal motion. The model requires only two input values at each minim a (or initial and final structures), representing a substantial reduction i n computational cost and has been able to predict the location of the trans ition state with very small error. (C) 1999 John Wiley & Sons, Inc.