Ab initio calculation of lattice dynamics in BeO

Abstract

Ground state lattice vibrational properties of wurtzite–BeO are reported using an ab initioplane-wave pseudopotential method. The ab initio results for the phonon dispersionrelations are in good agreement with the available experimental data. The only discrepancyobserved between experiment and present data for the longitudinal optic frequency at thecentre of the Brillouin zone for a displacement along the symmetry axis is expected to bedue to the indirect measurement of that mode in the experiment. The dielectric constant,the Born effective charges and the elastic constants for the compound are computed fromthe lattice dynamics. All of them agree well with the experimental results. The elasticconstants calculated using the phonon spectra agree reasonably well with the resultsfrom other first-principles calculations. The good agreement of the quantitiescalculated, with the experimental results pave the way for future studies on thecontribution of lattice vibrations to the pressure-induced phase transition in thiscompound. We try to understand the features of the phonon spectra from thecomponent-projected phonon densities of states and by analysing the contributions ofeach atom type towards each normal mode. We find that the phonon spectra ofBeO contains features common to some of the members with the same crystalstructure as well as to some of the members in the same alkaline earth oxide group.