Variational Principles for Expectations

Abstract

Variational principles for expectation values of physical quantites other than the energy are derived. The expressions implicitly require Green's-function estimations, and higher-order corrections are available. One principle involves a subsidiary minimization, and the other involves the difference between two quantities which are minimum at the stationary point; consequently, numerical computations can be made with both of these principles. As a simple example, the mean-square radius of the hydrogen atom for an incorrect wave function is corrected, with excellent results. Application is also made to the meansquare radius of a model triton.