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A critical review of the experimental data of elastic stiffness constants of AgGaX[sub 2] and CuInX[sub 2] (X = S,Se) chalcopyrites is given. Using the ab initio pseudopotential method, their elastic constants have been calculated from strain-energy and from strain-stress relationships. On the basis of the linear elasticity approximation, axial and total compressibilities as well as elastic anisotropy factors have been derived. The calculated results are compared with available experimental data and previous calculations based on phenomenological models. [ABSTRACT FROM AUTHOR]

First-principles density-functional approach was used to obtain the crystal parameters and phonon spectra of γ-Mg[sub 2]SiO[sub 4] (spinel and ringwoodite) as functions of pressure. The Grüneisen parameters at the F point were obtained and compared with the experimental data. Using quasiharmonic approximation, the total free energy of the crystal was calculated as a function of volume for several temperatures, hence, the bulk modulus and thermal expansion were found as a function of temperature. A good agreement between calculated and experimental values was obtained in a wide temperature range. [ABSTRACT FROM AUTHOR]

The first principles plane-wave pseudopotential calculations based on density functional theory were used to determine structural and electronic properties of CuInS[sub 2] semiconducting chalcopyrite. The Born effective charges were obtained using Berry phase method. Phonon dispersion relations were evaluated from Hellmann-Feynman forces with the direct method. The elastic constants were derived from the stress-strain relationships. The calculated quantities agree well with available experimental data. [ABSTRACT FROM AUTHOR]

We have presented ab initio study, based on density functional theory methods, of full-core edge dislocation impact on basic properties of 4H-SiC semiconductor. To enable calculations in periodic boundary conditions, we have proposed geometry with two dislocations with opposite Burgers vectors. For this geometry, which determines the distance between dislocations, we have estimated the creation energy per unit length of a single-edge dislocation. The radial distribution function has been used to assess the effect of the dislocations on the local crystal structure. The analysis of the electronic structure reveals mid-gap p states induced by broken atomic bonds in the dislocation core. The maps of charge distribution and electrostatic potential have been calculated, and the significant decrease in the electrostatic barriers in the vicinity of the dislocation cores has been quantified. The obtained results have been discussed in the light of previous findings and calculations based mainly on phenomenological models. [ABSTRACT FROM AUTHOR]

The magnetization distribution, its energetic characterization by the interlayer coupling constants and lattice dynamics of (001)-oriented Fe/Pt multilayers are investigated using density functional theory combined with the direct method to determine phonon frequencies. It is found that ferromagnetic order between consecutive Fe layers is favoured, with the enhanced magnetic moments at the interface. The bilinear and biquadratic coupling coefficients between Fe layers are shown to saturate fast with increasing thickness of nonmagnetic Pt layers which separate them. The phonon calculations demonstrate a rather strong dependence of partial iron phonon densities of states on the actual position of Fe monolayer in the multilayer structure. [ABSTRACT FROM AUTHOR]