Realistic Simulation of Valence-Band Photoemission Spectra by Using First-Principles Calculations on the Basis of FLAPW Method

In order to reproduce experimental photoemission spectroscopy (PES) data by using band structure calculations with linearized augmented-plane-wave method, we developed a new method to calculate the atomic-subshell photoelectron differential cross section (PE-DCS) of the valence band. PE-DCS was calculated to be the sum of the products of the partial density of states (PDOS) and the photoionization differential cross section (PI-DCS) of each atomic subshell. To construct an appropriate PDOS beyond the conventional muffin-tin sphere (MTS) PDOS, we proposed a “nearly-neutral atomic sphere”, which can be defined as a natural extension of MTS. Although the calculational method for atomic-subshell PI-DCS was the standard Hartree–Fock–Slater method, we developed a new computer code in order to deal with the unoccupied electron shells in the ground state of isolated atoms up to ∼10 keV. Details of the PE-DCS calculations were examined by using two simple examples of Na metal and NaCl, and then, the method was applied to hard x-ray PES (HX-PES) data of CuAlO₂. The experimental spectra were satisfactorily reproduced, demonstrating the potential applications of our method to HX-PES spectra of many compounds.