CRITICAL COMPARISON BETWEEN EQUATION OF MOTION-GREEN FUNCTION METHODS AND CONFIGURATION-INTERACTION METHODS - ANALYSIS OF METHODS AND APPLICATIONS
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A description is provided of the common conceptual origins of many-body equations of motion and Greens function methods in Liouville operator formulations of the quantum mechanics of atomic and molecular electronic structure. Numerical evidence is provided to show the inadequacies of the traditional strictly perturbative approaches to these methods. Nonperturbative methods are introduced by analogy with techniques developed for handling large configuration interaction calculations and by evaluating individual matrix elements to higher accuracy. The important role of higher excitations is exhibited by the numerical calculations, and explicit comparisons are made between converged equations of motion and configuration interaction calculations for systems where a fundamental theorem requires the equality of the energy differences produced by these different approaches. 1980 IOP Publishing Ltd.
