Green's-Function Theory of Photoionization

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Abstract
The generalized random-phase approximation (GRPA) developed for electron-scattering problems is applied to the photoionization of electrons from atoms. In contrast to some other attempts to apply many-body techniques to photoionization problems, we concentrate on the generalized linear-response function of the ion, not the atom. This allows us to incorporate both the change in the effective charge seen by the outgoing electron during the photoejection process and the core polarization of the inner electrons in a rigorous manner. The derivation leads quite naturally to a formally exact one-electron theory of photoionization. In addition, corrections to the one-particle picture can be generated in a natural way. We conclude by examining some of the lower-order corrections to this one-electron model.