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The cluster-expansion approach to the correlation problem, pioneered by Cocster, Kümmel, Cizek and Paldus, is extended to calculation of static and dynamic properties of many-fermion systems. Linear, inhomogeneous equations are obtained for properties of any order. A time-dependent formulation gives frequency-dependent properties, yielding excitation energies, transition probabilities, and (possibly) life times reminiscent of Green's function methods.
Hendrik J. Monkhorst (Thu,) studied this question.