Symmetry-adapted many-body perturbation theory: use of the wave operator matrix elements

Abstract

In this paper we develop a simple method for adapting the closed-shell many-body perturbation theory to an arbitrary point group symmetry taking account of various classes of diagrams exactly to all orders. The method consists in deriving a linear operator equation for the closed-shell wave-operator W which is then symmetry-adapted to the pertinent point group G. It is shown that the system of equations thus derived enables one to include orbital-diagonal h-h, p-p and h-p ladders to all orders in a perturbative framework. The way to generalise the method through inclusion of a larger classes of diagrams to all orders is also indicated. Finally, the connection of the present mode of development with the non-perturbative coupled-cluster formalisms is briefly indicated.