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We report the first-principles calculation results on the structural and elastic properties of BeSxSe1−x alloys. These are done using the density functional theory within the local density approximation and employing virtual-crystal approximation. It is found that the lattice parameter, the phase transition pressure and elastic constants (and their derivatives with respect to the pressure) follow a quadratic law in x.

The lattice dynamics and the elastic properties of the ternary AlAs x Sb 1−x alloy have been studied using the density-functional perturbation theory within the local density approximation and employing the virtualcrystal approximation. We study the variation of the optical phonon frequencies (ω TO and ω LO ), the high-frequency (ε ∞ ) and static (ε 0 ) dielectric coefficients, the dynamic effective charge (Z * ) and the elastic constants (C 11 , C 12 , C 44 ) as a function of the composition (x) and the pressure. We have also predicted the behavior of the optical and acoustical phonons with composition x at the X and L high symmetry points under pressure and determined the Grüneisen parameter. We have found that no mechanical instabilities are associated with the structural transition at high pressures for all compositions.

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