Theoretical calculations of x-ray-absorption spectra of copper in La2CuO4 and related oxide compounds

We report the results of theoretical calculations of copper K-edge x-ray-absorption near-edge spectra (XANES) in La2CuO4 and related oxides Cu2O, CuO, and KCuO2. The final bound states were obtained from the self-consistent-field discrete-variational X method (SCF DV X ), and continuum states were found by the multiple-scattering method using the muffin-tin truncation of the SCF DV X potentials. Composition of the final-state wave functions was analyzed. The 1s ionization potentials of the three reference compounds obtained from the SCF DV X 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 Cu2O, CuO, and KCuO2 were reproduced satisfactorily by our calculations along with their relative energy positions. Our calculated polarized XANES of La2CuO4 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.