CRYSTALLINE POTENTIAL FOR PHOTOELECTRON SCATTERING PHASE-SHIFT CALCULATIONS AND X-RAY ABSORPTION-SPECTRA OF TI IN CRYSTALS

X-ray absorption spectra (XAS) of Ti in crystals of Ti metal, TiC, TiN and TiO2 rutile are calculated in EXAFs and XANEs regions. Single, double and triple photoelectron scattering processes are included through the spherical-wave formalism and the crystalline muffin-tin (MT) potential model, which employs a Hartree-Fock exchange interaction between photoelectron and core electrons inside MT spheres. Overall agreement of the theoretical and experimental spectra is obtained on the absolute photon energy scale. This result enables one to treat the experimental XAFS without using adjustable parameter E0. The neutral-atoms approximation is shown to be adequate for the phase-shift calculations in XAS theory for both metals and insulators. A comparison of Ti KXAFS of Ti metal calculated by means of various exchange-correlation potentials for the photoelectrons inside MT spheres is carried out. The best results are shown to be provided by Hartree-Fock and Dirac-Hara exchange potentials.