SIZE CONSISTENCY OF AN ALGEBRAIC PROPAGATOR APPROACH

The size consistency property of a general algebraic propagator method referred to as intermediate-state representation (ISR) is discussed. In this method intermediate states \<(Psi)over tilde>(J)] constructed by a specific orthonormalization procedure from the set of ''correlate d excited states'' (C) over cap(J)/Psi(0)(N)] used to represent the Ha miltonian (H) over cap. Here (C) over cap(J) denotes a physical excita tion operator and \Psi(0)(N)] is the N-electron ground state. The ISR secular equations are shown to be separable, that is, they decouple in to independent (local) sets of equations for a system consisting of no ninteracting (separate) fragments. This result follows from a general factorization theorem for the intermediate states. Separability is a s ufficient condition for size consistency. (C) 1996 John Wiley & Sons, Inc.