SPECTRAL DENSITY DISTRIBUTION OF AN N-ELECTRON HAMILTONIAN IN A FINITE-DIMENSIONAL AND SPIN-ADAPTED MODEL SPACE

Expressions for moments of spectral density distributions of a many-el ectron Hamiltonian defined in a finite-dimensional, antisymmetric, and spin-adapted model space (as, e.g., a full configuration interaction space) are derived. The moments are expressed in terms of combinations of two-electron integrals corresponding to a symmetric (a two-electro n singlet) and antisymmetric (two-electron triplet) two-electron wave functions. A diagrammatic approach based on Hugenholtz-type diagrams a nd leading to a simple and universal classification scheme of the term s appearing in the expression for a specific moment is proposed. (C) 1 995 John Wiley & Sons, Inc.