Regularized diabatic states and quantum dynamics on intersecting potential energy surfaces

The importance of diabatic electronic states for a quantum-dynamical treatment of conically intersecting potential energy surfaces is well known. An efficient construction scheme of approximately diabatic states is discussed which focuses on the removal of the singular derivative couplings and often relies on information from the potential energy surfaces alone. Thus an accuracy is achieved which is comparable to that of the Born - Oppenheimer approximation for widely spaced electronic states. New applications are presented for nitrogen dioxide and acetylene.