A unitary wave operator exp(G) is used to relate a multiconfigurational reference function Φ to the full, potentially exact, electronic eigenfunction Ψ=exp(G)Φ. If the reference function Φ is of a generalized complete-active-space (CAS) form, then the energy, computed as 〈Φ‖exp(−G)H exp(G)‖Φ〉 is …