Browsing by Author "Litimein, F."

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Prediction Study of the Mechanical and Thermodynamic Properties of the (R Sm, Eu, Gd, and Tb) Compounds
(Springer/plenum Publishers, 2013) Mekkaoui, F.; Litimein, F.; Khenata, R.; Merabiha, O.; Bouhemadou, A.; Varshney, D.; Rached, D.
The structural, elastic, and thermodynamic properties of the cubic anti-perovskite (R = Sm, Eu, Gd, and Tb) compounds have been investigated using first principles full-potential augmented-plane wave plus local orbitals (FP-APW+lo) method with the generalized gradient approximation. The ground-state quantities such as the lattice parameter, bulk modulus, and its pressure derivative, as well as elastic constants are estimated. Computed equilibrium lattice constants agree well with the available experimental data. The full set of first-order elastic constants and their pressure dependence, which have not been calculated or measured yet, have been determined. The elastic moduli increase linearly with increasing pressure and satisfy the generalized elastic stability criteria for cubic crystals under hydrostatic pressure. The shear modulus, Young's modulus, and Poisson's ratio are calculated for ideal polycrystalline aggregates. The Debye temperature is estimated from the average sound velocity. From the elastic parameter behavior, it is inferred that cubic anti-perovskites are ductile in nature and that the bonding is predominantly of an ionic nature. Following the quasi-harmonic Debye model, the temperature effect on the lattice constant, bulk modulus, heat capacity, and Debye temperature is calculated reflecting the anharmonic phonon effects.
Structural, Elastic, Electronic and Optical Properties of Cu3tmse4 (Tm = V, Nb and Ta) Sulvanite Compounds Via First-Principles Calculations
(Amer Scientific Publishers, 2013) Bougherara, K.; Litimein, F.; Khenata, R.; Ucgun, E.; Ocak, H. Y.; Ugur, S.; Bin Omran, S.
The structural and optoelectronic properties of the cubic Cu3TMSe4 (TM = V, Nb and Ta) sulvanite compounds have been calculated using a full-potential augmented plane wave plus local orbitals (FP-APW + lo) method within the density functional theory. The exchange-correlation potential was treated with the generalized gradient approximation of Wu and Cohen (WC-GGA) to calculate the total energy. Moreover, the Engel-Vosko generalized gradient approximation (EV-GGA) and the modified Becke-Johnson potential (TB-mBJ) were also applied for the electronic and optical properties. The ground state properties, including, lattice constants, bulk modulus are in reasonable agreement with the available experimental and theoretical data. The elastic constants C-ij are computed using the total energy variation versus strain technique. The polycrystalline elastic moduli, namely; shear modulus, Young's modulus, Poisson's ratio and anisotropic factor were derived from the obtained single-crystal elastic constants. As a result, brittleness behaviour of these compounds is interpreted via the calculated elastic constants C-ij. The calculations of the electronic band structure show that these compounds have an indirect energy band gap (R-X) and the TB-mBJ approximation yields larger fundamental band gaps compared to those of WC-GGA and EV-GGA. The dielectric function, refractive index, extinction coefficient, reflectivity, and energy loss function were calculated for radiation up to 45 eV.