RESPONSE-FUNCTION APPROACH TO THE DIRECT CALCULATION OF THE TRANSITION-ENERGY IN A MULTIPLE-CLUSTER EXPANSION FORMALISM

In this paper, we have developed a response function approach to the direct determination of transition energy in a multiple-cluster expansion formalism. We adopt a time-independent formalism in a way reminiscent of the Fourier-transformed version of a response-function theory. The formalism has been used to describe specifically the linear response, and compact and usable formulae have been derived for the calculation of excitation energy and dynamic polarisability of closed-shell systems. Extension of the method for calculating higher order response functions and ionisation potentials is straight-forward. © 1979.