Theoretical calculations of x-ray-absorption spectra of copper inLa2CuO4and related oxide compounds

We report the results of theoretical calculations of copper K-edge x-ray-absorption near-edge spectra (XANES) in ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ and related oxides ${\mathrm{Cu}}_2$O, CuO, and ${\mathrm{KCuO}}_2$. The final bound states were obtained from the self-consistent-field discrete-variational Xα method (SCF DV Xα), and continuum states were found by the multiple-scattering method using the muffin-tin truncation of the SCF DV Xα potentials. Composition of the final-state wave functions was analyzed. The 1s ionization potentials of the three reference compounds obtained from the SCF DV Xα transition-state calculations were used to set up the relative energy scale for the calculated cross section. The principal features of measured Cu K-edge XANES for ${\mathrm{Cu}}_2$O, CuO, and ${\mathrm{KCuO}}_2$ were reproduced satisfactorily by our calculations along with their relative energy positions. Our calculated polarized XANES of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ were compared with measured spectra, and two shakeup features were identified with radiation polarized along the crystal c axis. By quantitatively comparing the measured spectra with a model based on our calculated cross sections, their intensities were found to be ∼24% and 10% of the main transition with shakeup energies of 5.7 and 9.5 eV, respectively. We suggest that these multielectron excitation features involve Cu 3d→4p transitions.