DFT calculations of energy dependent XPS valence band spectra

Abstract

In the past few years it became regularly possible to measure valence band X-ray photoelectron spectra (XPS) using variable excitation energies. This ranges from UV-light to conventional X-ray sources (like Al Kα) all the way to synchrotron radiation with energies of several keV. In order to explain the observed variations in intensity with respect to the excitation energy, we performed XPS calculations using the WIEN2k code. The new PES module computes the XPS spectra using a combination of partial density of states times excitation-energy-dependent atomic-orbital cross sections. It considers as additional correction the charge fraction of the corresponding orbital located inside the atomic spheres. The resulting XPS spectra are compared with experimental data for SiO2, PbO2, CeVO4, In2O3 and ZnO at different excitation energies and in general good agreement between the simulated and experimental spectra has been achieved. In some cases significant unexpected contributions like Pb-6d in PbO2 or Zn-4p in ZnO appear and explain some features in the experimental spectra which previously have not been identified.