Energies and Derivative Couplings in the Vicinity of a Conical Intersection Using Degenerate Perturbation Theory and Analytic Gradient Techniques. 1

Abstract

Analytic gradient techniques in conjunction with degenerate perturbation theory are used to analyze the energetics and the derivative couplings in the vicinity of a conical intersection. The precision of the analytic gradient based evaluation of the derivative couplings in the vicinity of a conical intersection is established. An approach for the rigorous treatment of two-dimensional Jahn-Teller problems in the absence of C3v symmetry is suggested.