Perfect pairing valence bond generalization of self-consistent electron pair theory

A generalization of the self-consistent electron pairs (SCEP) method for correlated wave functions is presented which makes possible the use of multiconfiguration reference wave functions that have the form of a generalized valence bond, perfect pairing (GVB/PP) wave function. All singly and doubly substituted configurations relative to this reference are included, though the sets of configurations arising from a given orbital substitution are restricted to occur in the correlated wave function with the same relative importance as the corresponding configurations in the reference wave function. The computational manipulations of this new procedure are essentially the same as basic SCEP, but the generalization provides for the treatment of systems where a Hartree–Fock reference wave function is inappropriate. These would include i reactive systems that involve changes in bonding and also weakly interacting systems where higher order correlation effects are necessary.