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

Abstract

We report the results of theoretical calculations of copper K-edge x-ray-absorption near-edge spectra (XANES) in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ and related oxides ${\mathrm{Cu}}_{2}$O, CuO, and ${\mathrm{KCuO}}_{2}$. The final bound states were obtained from the self-consistent-field discrete-variational X\ensuremath{\alpha} method (SCF DV X\ensuremath{\alpha}), and continuum states were found by the multiple-scattering method using the muffin-tin truncation of the SCF DV X\ensuremath{\alpha} potentials. Composition of the final-state wave functions was analyzed. The 1s ionization potentials of the three reference compounds obtained from the SCF DV X\ensuremath{\alpha} transition-state calculations were used to set up the relative energy scale for the calculated cross section. The principal features of measured Cu K-edge XANES for ${\mathrm{Cu}}_{2}$O, CuO, and ${\mathrm{KCuO}}_{2}$ were reproduced satisfactorily by our calculations along with their relative energy positions. Our calculated polarized XANES of ${\mathrm{La}}_{2}$${\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 \ensuremath{\sim}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\ensuremath{\rightarrow}4p transitions.