Systematic treatment of correlations in a generalized Hartree-Fock approximation

The HartreeFock (HF) approximation is generalized to the study of n-particle states, taking correlation effects in interacting quantum-mechanical many-particle systems systematically into account. The case of n = 2 is developed explicitly. It is shown that the form of the HF equations remains essentially the same as in the usual formulation, but with appropriate interpretations of various parameters in terms of n-particle, rather than single; particle, states. We show results of calculations for model systems that illustrate the power of the method when compared to ordinary versions of the HF treatment.