Developments in the <i>n</i>‐electron valence state perturbation theory

Abstract

Abstract A short summary of the n‐ electron valence state perturbation theory (NEVPT) is provided, and the defects inherent in cases of quasi‐degeneration are underscored. A new version of the theory, called QD‐NEVPT, based on quasi‐degenerate perturbation theory, is presented. The new theory introduces an effective interaction among the zero‐order wave functions and overcomes the difficulties of state‐specific NEVPT. An application concerning the interaction among the π → π* and Rydberg singlets of formaldehyde is presented. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006