First principles calculation of Fe L 2,3-edge X-ray absorption near edge structures of iron oxides

Abstract

X-ray absorption near edge structure (XANES) at L 2,3-edge of 3d transition elements is dominated by strong correlation effects among 2p core hole and 3d electrons. In the present study, we have performed systematic configuration interaction (CI) calculations in order to reproduce and interpret Fe-L 2,3 XANES of FeO, LaFeO 3 and SrFeO 3. Relativistic four components wave functions were obtained by solving Dirac equations with density functional theory. CI calculations were made using the relativistic molecular orbitals instead of atomic orbitals, which enables inclusion of the O-2p orbital contributions through covalency. The oscillator strength of the electric dipole transition was then computed. Experimental XANES spectra of three compounds were satisfactorily reproduced by the theoretical spectra obtained for (FeO 6) m- clusters in octahedral symmetry. Chemical shifts between compounds were quantitatively reproduced as well. Component analysis of CI was systematically made in order to analyze the origin of differences in spectral shapes.