On a Green’s Function Method for the Calculation of Ionization Spectra in the Outer and Inner Valence Region

Abstract

The one-particle Green’s function contains all information about ionization spectra and electron affinities, in particular the information on the energies and relative intensities of the lines. The vibrational structure as well as vibronic coupling phenomena can also be obtained from the Green’s function. It turns out that the structure of the ionization spectrum is very different in general in the outer and inner valence region. In the inner valence region the molecular orbital model of ionization may break down completely. The intensity then becomes distributed over numerous lines and a main line ceases to exist. In this energy region due to the high density of states a computational method should be used which correctly gives the general structure of the spectra - such a method is the two-particle-hole Tamm-Dancoff Green’s function approximation (2ph-TDA), whereas in the outer valence region high accuracy is required. This is supplied by an extended 2ph-TDA method (e-2ph-TDA) or a method especially adapted to this energy range, the outer valence Green’s function or OVGF method.