Electron propagator studies of molecular anions

Electron propagator (EP) or Green's function (GF) methods have been successfully employed to compute electron affinities for a large number of molecules having either a closed‐shell or single‐valence‐hole dominant electronic configuration. The accuracy of such calculations, if carried out through third order, has often been comparable to that of reasonable configuration interaction (CI) calculations. However, as a computational tool, EP methods have not yet been adequately developed in relation to general open‐shell molecules and atoms, and only recently have they begun to be generalized to describe states having two or more dominant configurations. Thus although GFs look promising as methods for ab initio calculation, much formal and programming work remains to be done before this approach can be said to compete with CI methods. On the other hand, GFs provide us with a mechanism for focusing on the one‐electron (EP) or two‐electron [polarization propagator (PP)] features of any problem. It is this fact that makes GFs an attractive route for developing chemical models which may or may not make use of experimental data. Although such a viewpoint has been widely used in solid‐state physics, not enough work has been done on making models based upon the EP or PP. In this article, both the computational and formal history of GFs, as they apply particularly to molecular anion studies, are overviewed. The author's opinions concerning the current status and future development of the area constitute a large part of the presentation.