Abstract. We present a comprehensive ab initio study of all non fully symmetric Γ point lattice vibrations in CaV₂O₅. The characteristics of CaV₂O₅ are a half-filled upper electron band and a ladder-like crystal structure. Adopting the frozen-phonon approach we calculate and analyze in detail the phonon eigenfrequencies and eigenvectors. The corresponding spectra of inelastic light scattering are computed for all Raman-active modes, including their resonance behavior as a function of incoming light. Our results allow for a qualitative and quantitative understanding of the phonon-related features in experimental optical excitation spectra. The theoretical data are employed to discuss available measurements and provide an improved assignment of the observed modes with respect to symmetry and displacement patterns. Electron hopping parameters and spin–spin exchange matrix elements are evaluated from the electronic bands. The changes in these parameters upon atomic displacements along the phonon eigenvectors are analyzed semiquantitatively, yielding the effect of lattice vibrations on charge and spin degrees of freedom. It is discussed how all the obtained results differ from the ones in the quarter-filled NaV₂O₅ compound due to differences in the electron band structure and in the chemistry.

Received 30 July 2009
Published 5 November 2009