Coupled Cluster Approaches to Many-Electron Correlation Problem

Abstract

The origins, basic ideas and methodological developments of the coupled cluster approach (CCA) to the atomic and molecular many-electron correlation problem are briefly outlined. A rudimentary derivation of basic concepts of the CCA is attempted exploiting only very general algebraic concepts and the idea of an effective Hamiltonian. The relationship with other approaches to the correlation problem is pointed out. An extension of the CCA to quasi-degenerate cases is briefly contemplated and a generalization of the Davidson correction to a multi-reference case is suggested.