Modified coupled cluster amplitudes

Abstract

The factorization of amplitudes of multiple excitations from those of elementary (single and double) excitations is only reliable when excitation energies are nearly additive. Such deviations from additivity may be important, especially in solid-state physics problems. Instead of introducing many-body operators in the coupled-cluster expansion, one may take into account the effect of these deviations from the additivity of excitation energies by proper energy-dependent corrections to the usual product of amplitudes. Their efficiency is illustrated on several model problems where the traditional approach gives poor results. © 1995 John Wiley & Sons, Inc.