Extended-Average-Energy Method for Perturbation Problems

Abstract
An extended‐average‐energy (eae) method for approximating the first‐order perturbation wavefunction ψ1 is presented. This method gives the best ψ1 of the form f(q0, where f is a function of a single variable q occuring in the perturbation. In the case of a one‐dimensional problem our ψ1 is exact. A procedure is suggested for extending this treatment even further to obtain the exact ψ1 for multidimensional problems. Application is made to the polarizability of atomic hydrogen and electron correlation in the helium isoelectronic sequence.