Core-hole effects on the ELNES of absorption edges in SrTiO3.

Near-edge structures of absorption edges in electron energy-loss spectra (ELNES) of SrTiO(3) were calculated and compared to experimental inelastic electron scattering data. The goal of this study was to investigate final-state effects on the electronic structure. Two theoretical approaches were applied: density-functional theory with a band-structure supercell method and a real-space multiple-scattering cluster approach. Within both techniques, the Z+1 approximation was used to model the core hole generated by the inelastic scattering process. For the band-structure calculations, supercells of (SrTiO(3))(n)(n=1,4,8,16) composition with three-dimensional periodic boundary conditions were applied. The influence of supercell size and shape on calculated site- and symmetry-projected local densities of unoccupied states is assessed quantitatively. Relevant convergence criteria are the length scale set by the spatial extension of the valence-electron screening cloud around the core hole, and the interaction energy of neighbouring core hole centres. For a sufficiently large supercell size, the Z+1 approximation yields a reasonable description of the local densities of unoccupied states probed by the energy losses of inelastically scattered electrons of the Ti L(3)-, O K- and Sr L(3)-absorption edges. The quantitative equivalence of ELNES information extracted from the multiple-scattering cluster calculations and the band-structure supercell calculations is demonstrated. Discrepancies between theoretical and experimental results are discussed.