We have carried out a first-principles total-energy calculation of the structural and the elastic properties for the series of boron compounds BP, BAs, and BSb. We have applied the augmented plane-wave plus local-orbitals method with both the local-density approximation (LDA) and the generalized gradient approximation (GGA). Since there have been no previous theoretical or experimental determinations, our calculations provide the first available information on the elastic constants of these materials. The elastic constants have been derived by the stress-strain relation. We have calculated all of the equilibrium structural parameters for both phases: rock salt and zinc blende structures.

The structural, electronic and thermodynamic properties of PbSe 1−x S x , PbSe 1−x Te x and PbS 1−x Te x ternary alloys have been calculated using the full-potential linearized-augmented plane wave method. The exchange and correlation potential is treated by the generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof parameterization. Moreover, the Engel-Vosko GGA formalism is also applied to optimize the corresponding potential for band structure calculations. A nonlinear dependence of the effect of the concentration (x) on the lattice constants, bulk modulus and band gaps is found. The microscopic origins of the band gap bowing parameter have been discussed. Moreover, the thermodynamic stability of the studied alloys is investigated by means of the miscibility critical temperature.

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The structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and BeTe using full-potential linear augmented plane wave (FP-LAPW) method are investigated. The exchange-correlation energy within the local density approximation (LDA) and the generalized gradient approximation (GGA) are described. The calculated structural parameters are in reasonable agreement with the available experimental and theoretical data. The electronic band structure shows that the fundamental energy gap is direct (L-L) for all the compounds. Thermal effects on some macroscopic properties of these compounds are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the lattice constant, bulk modulus, heat capacity, volume expansion coefficient and Debye temperature with temperature and pressure are obtained successfully. The effect of spin-orbit interaction is found to be negligible in determining the thermal properties and leads to a richer electronic structure.

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