Quasi-Particle Properties of Hole Levels in Solids and Adsorbate Systems

This section will contain less analytical and more straightforward presentation of current experimental and theoretical results and ideas. The field is developing extremely rapidly and fairly little has been done so far in terms of quantitative calculations on real systems. Most of the theoretical investigations have been in the form of one-electron calculations for molecules and clusters, or many-body calculations on model systems. We shall discuss a number of cases where hole spectra in extended systems are strongly influenced or, in certain regions, even dominated by atomic-like, local excitations, with the particular aim of presenting an overview of unifying aspects. 

Quasi-Particle Properties of Hole Levels in Solids and Adsorbate Systems 

It seems that cases of strong coupling can be found in e.g. 3 d-TM s and probably also in 3 d-TM compounds and in many adsorbate systems. In such cases, the overlap between the localized orbital and the valence orbitals is quite large. The screening process then rather corresponds to a pronounced shift of the bonding charge towards the central metal ion or towards the adsorbate, and the lowest line picks up most spectral strength and also becomes the main line. 

Finally, Fig. 58 e may illustrate intra-3 d-band fluctuation and decay of a 3 d-valence hole in metallic Ni. This process is probably one of the essential elements in the description of the valence band photoelectron spectrum which seems to show 3 d-band narrowing, decreased splitting of the majority and minority spin bands and a pronounced shake-up structure about 6 eV below the Fermi level (see e.g.143 175) and references therein, and also Sect. 8.3.4). 

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