ELECTRON PROPAGATOR THEORY WITH THE GROUND-STATE CORRELATED BY THE COUPLED-CLUSTER METHOD

Ground state electron correlation is introduced into the one-particle propagator via coupled cluster theory. This defines a similarity trans formation of the Hamiltonian, which leads to the complete separation o f the ionization and electron attachment aspects of the propagator. Th e latter makes it possible to solve for each property independently. F urthermore, the frequency (or energy) dependence which characterizes p ropagator theory is eliminated by introducing a wave operator formalis m. It is shown that this procedure is equivalent to the summation of c ertain types of terms in the electron propagator perturbation expansio n to infinite order. Finally, the resulting equations are found to be equivalent to those of the Fock-space coupled-cluster (or equivalently the equation of motion coupled-cluster) method, which provides an exp licit wave function for each state, demonstrating the connection betwe en these different approaches for the calculation of ionization potent ials and electron affinities. Understanding this relationship permits new and powerful approximations to be proposed. (C) 1993 John Wiley & Sons, Inc.