Calculations of Clean and Adsorbate Covered Metal Surfaces and their Core-Level Photoemission Spectra

Abstract: The present thesis is concerned with the theoretical study of x-ray photoemission spectra from clean and adsorbate-covered metal surfaces. The main tool is ab initio density functional (DFT) total energy calculations. The first part gives an overview of the theoretical treatment of x-ray photoemission with our present contributions highlighted, and an introduction to DFT theory and computational techniques for obtaining total energies. The second and main part of the thesis contains the original research papers. In a major part of these, DFT calculations are combined with and compared to experimental photoemission spectra in order to investigate both the local geometric as well as electronic structure. Paper I and II consider clean and CO-covered Rh(111) surfaces, paper IV considers the clean Al(100) and Al(111) surfaces both theoretically and experimentally, and paper V combines experimental techniques and theoretical modeling to investigate the adsorption of Na on Al(100) in a (sqrt(5) x sqrt(5))R27 structure. In all cases we find that ab initio calculations predict the experimental findings well, both with regard to geometries and with regard to chemical shifts and other electronic properties. Furthermore, we find that chemical shifts usually depend on the local geometry in a rather sensitive way. Thus, by combining experiment with theoretical modeling, very precise geometrical information can be obtained. In paper III, we leave the common approximation of treating the core-electron vacancy as a structure-less entity as in the Mahan-Nozières-DeDominicis (MND) model and takes its internal spin and possible orbital angular momentum degrees of freedom into account. We treat the additional symmetry-dependent interactions by leading order cumulant and self energy expansions and apply our theory to both an sp-bonded metal (Al (2p)) as well as 4d metals (Rh (3d), Pd (3d)). In the case of Al and Pd the effects of core-level degeneracy are small, but for Rh we find important modifications. When the effects of core-level degeneracy are included, the theoretical line-shapes agree rather well with experiment.