On the connectivity of seams of conical intersection: Seam curvature

The seam of conical intersection of two electronic states is said to be curved when the span of the basis vectors describing the branching plane varies along the seam. In this work degenerate perturbation theory is used to determine an approximately diabatic Hamiltonian that can reliably reproduce the potential-energy surfaces in the vicinity of a point of conical intersection. This Hamiltonian provides a rigorous description of seam curvature, and a means for obtaining the full ( N int − 2 ) -dimensional seam of conical intersection connected to a point of conical intersection.