ELASTIC-CONSTANTS AND ELECTRONIC-STRUCTURE OF BERYLLIUM CHALCOGENIDESBES, BESE, AND BETE FROM FIRST-PRINCIPLES CALCULATIONS

We use an ab initio total energy pseudopotential technique within the local-density aproximation to determine the full set of first-order el astic constants of BeS, BeSe, and BeTe, which have not been establishe d experimentally. For BeS we obtain C-11=1.84, C-12=0.75, and C-44=0.9 9 Mbar. For BeSe and BeTe we obtain C-11=1.49, 1.11; C-12=0.59, 0.43; and C-44=0.81, 0.60 Mbar, respectively. We also calculate the bulk mod ulus, the optical phonon frequency at Gamma, and we present a study of the electronic band structure of those compounds. The calculated bulk moduli agree well with previous experimental and theoretical values.