Construction scheme for regularized diabatic states

A simple construction scheme for quasidiabatic electronic states implemente d earlier for a Jahn-Teller situation [J. Chem. Phys. 110, 9371 (1999)] is extended to the case of a seam of symmetry-allowed conical intersections. I t is based on the idea of removing only the singular part of the nonadiabat ic coupling elements, leading to the notion of "regularized" diabatic state s. Explicit working equations are given for the resulting potential energy matrix which require only information from the adiabatic potential energy s urfaces alone. The approach is tested for the photodissociation of H2S and O-3 and very good agreement with reference data from the literature is foun d. (C) 2001 American Institute of Physics.