Electronic structure of LaNiO3-x thin films studied by x-ray photoelectron spectroscopy and density functional theory

We present the experimental and theoretical study of x-ray photoelectron spectroscopy spectrum of LaNiO3-x thin films deposited onto a (100)-plane oriented NdGaO3 substrate by applying a reactive dc magnetron sputtering technique. The crystal calculations carried out within pure density functional theory (DFT) approximation properly reproduce the delocalized valence band showing the suitability of homogeneous electron gas model, whereas hybrid DFT/Hartree-Fock (HF) calculations work out in the core region indicating the localized nature of core electrons. The significance of spin-orbit coupling to the electronic structure of LaNiO3 is revealed by relativistic molecular HF study allowing to theoretically identify the doublet splitting of La 5p. Electron-density difference map indicates a different nature of La-O and Ni-O chemical bonds in LaNiO3 while the Mulliken population analysis adds information about the charge distributions and overlap populations between separate atoms.