Pair functions and biorthonormal orbitals in the context of the method of moments. I

Abstract

A pair-function approach is formulated within the framework of the method of moments. The strong orthogonality constraint, which is found to the main defect of the separated pair approximation, is avoided. Tractable formulae are obtained by using slightly different wave functions on the left and the right-hand side when constructing matrix representations of the Schrödinger equation.