Electron binding energies of anionic alkali metal atoms from partial fourth order electron propagator theory calculations

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Abstract
Ionization energies of Li−, Na−, K−, Rb−, and Cs− are calculated with ab initio electron propagator theory. Effective core potentials are employed for K, Rb, and Cs. Third order diagonal self-energy corrections to Koopmans’s theorem are augmented with fourth order terms that are easily determined from by-products of a third order calculation. This partial fourth order procedure is derived using superoperator theory. The superiority of this method to an outer valence diagonal approximation is demonstrated for these systems. Covergence of results with respect to the order of electron interaction in the propagator self-energy and with respect to basis set improvement is studied. Agreement to within 0.1 eV of experiment is achieved. Remaining sources of error are analyzed.