Analysis of Core-Hole Effect in Cation L2,3-Edge of MgO, α-Al2O3 and SiO2 Based on DV-Xα Cluster Calculations

In order to clarify the effect of a core hole in the cation L2,3-edge of electron energy-loss near-edge structures (ELNES) and X-ray absorption near-edge structures (XANES), the photoabsorption cross section (PACS) and the partial density of stats (PDOS) are calculated for MgO, α-Al2O3, SiO2 (α-quartz) based on the DV-Xα cluster calculations in the absence and presence of a core hole. It is found that the PDOS is a good approximation of the PACS and the major spectral features are well reproduced by the Slater's transition state, in which one half of a core electron is excited to an unoccupied orbital. The absolute transition energy calculated by the spin-polarized transition state is in excellent agreement with those estimated from the XANES spectra. The strongest peak that appears near the A1 L2,3-edge is found to originate from the presence of a core hole. Such an effect is less significant in MgO and α-quartz. The electronic relaxation due to the presence of a core hole was characterized by the localization of unoccupied molecular orbitals and evaluated quantitatively by calculating the localization index of these orbitals. The difference in the magnitude of core-hole effects in these oxides were well understood by the difference in the structural and chemical environment of excited atoms such as cation-cation distances and the coordination numbers.