Optical properties, electron-phonon coupling, and Raman scattering of vanadium ladder compounds

The electronic structure of two V-based ladder compounds, the quarter-filled NaV2O5 in the symmetric phase and the isostructural half-filled CaV2O5, is investigated by ab initio calculations. Based on the band structure we determine the dielectric tensor «svd of these systems in a wide energy range. The frequencies and eigenvectors of the fully symmetric Ag phonon modes and the corresponding electron-phonon and spin-phonon coupling parameters are also calculated from first principles. We determine the Raman scattering intensities of the Ag phonon modes as a function of polarization and frequency of the exciting light. All results—i.e., shape and magnitude of the dielectric function, phonon frequencies, and Raman intensities—show very good agreement with available experimental data.