Variational Form of Van Vleck Degenerate Perturbation Theory with Particular Application to Electronic Structure Problems

Abstract

The variational equivalent of Van Vleck degenerate perturbation theory is derived. As an example we treat the Stark effect for the 2s and 2p states of a hydrogenic atom. Other applications involving angular momentum degeneracy as well as electronic and nuclear permutation degeneracy are discussed. The existence of interchange theorems is also noted.