Geometric and electronic structure effects in polarized VK-edge absorption near-edge structure spectra of V2O5

Experimental and theoretical polarized V K-edge spectra of V2O5 are presented. By analyzing experimental spectra, we find that quadrupole transitions are significant, although not dominant at the pre-edge region. Real-space multiple-scattering calculation, relying on a non-self-consistent muffin-tin potential, can account for the basic polarizations trends and for peak heights and positions of the experimental spectra. However, important differences between theory and experiment occur for low-photoelectron energies. Lack of selfconsistency, muffin-tin form of the potential, and complex core-hole effects are identified as possible sources of this discrepancy. We argue that this deficiency of the theory would not get revealed if unpolarized spectra were investigated only. Cluster-size convergence of the calculated spectra is not uniform and it depends on the polarization. By performing model calculations we find, that deviations of the V2O5 structure from a perfect horizontal symmetry are much less significant for the shape of the spectrum than deviations from the vertical symmetry. For generating the distinct prepeak in the spectrum, which is polarized along the vertical axis, both short V-O bond length and deviations from inversion symmetry are crucial. The high-energy tail of the spectrum (photoelectron energies more that 30 eV) seems to be generated by scattering from more distant atoms. [S0163-1829(99)10843-9].