Correction of Configuration-Interaction Wavefunctions by Perturbation Theory

Abstract

It is shown that a natural choice of the zeroth‐order Hamiltonian for a configuration‐interaction or a multiconfigurational self‐consistent‐field wavefunction, has interesting implications for the Rayleigh—Schrödinger perturbation corrections to the wavefunction and the energy of a system. In particular it is shown that the odd‐order corrections to the energy vanish. In addition we demonstrate two other properties of the perturbation expansion based on a projection operator definition of the zeroth‐order Hamiltonian.