In this present work, we are interesting on the first-principles study of structural, elastic, electronic and dielectric properties of BeSxSe1-x which are potentially good materials for technological applications and are a promising material for blue-green laser diodes and laser-emitting diodes. All calculations were performed within the framework of the density-functional theory DFT [1,2] with the local density approximation LDA for the exchange-correlation energy as implemented in the ABINIT code [3 ]. We have used the Teter and Pade parameterization [4] for LDA. Only the outermost electrons of each atom were explicitly considered in the calculation, and the effect of the inner electrons and the nucleus (the frozen core) was described within a pseudopotential scheme. We used the Hartwigzen Goedecker Hutter scheme[5] to generate the norm-conserving nonlocal pseudopotentials, which results in highly transferable and optimally smooth pseudopotentials. A plane-wave basis set was used to solve the Kohn-Sham equations in the pseudopotential implementation of the DFT-LDA.
The Brillouin zone integrations were replaced by discrete summations over a special set of k-points using the standard k-point technique of Monkhorst and Pack [6].
For the treatement of the alloy disorder, we have used the virtual crystal approximation VCA [7], in which one studies the crystal with the primitive periodicity, but composed of virtual atoms that interpolate between the behavior of atoms in the parent compounds.
We have calculated the elastic properties of these compounds by computing the components of the stress tensor for small strains using the method developed by Nielsen and Martin [8]. The plane -wave energy cutoff to expand the wave functions is set to be 90 Hartree (1 Hartree = 27.211396 eV). Integrals over the Brillouin zone are performed using Monkhorst-Pack scheme [9] where the k-point mesh used is (8 X 8 X 8).

References:
1. P. Hohenberg, W. Kohn, Phy Rev. B136, 864
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