F. Soyalp

Electronic structure calculations of rare-earth intermetallic compound YAg using ab initio methods

Abstract The structural, elastic and electronic properties of YAg-B2(CsCl) were investigated using the first-principles calculations. The energy band structure and the density of states were studied in detail, including partial density of states (PDOS), in order to identify the character of each band. The structural parameters (lattice constant, bulk modulus, pressure derivative of bulk modulus) and elastic constants were also obtained. The results were consistent with the experimental data available in the literature, as well as other theoretical results.

Structural, electronic and elastic properties of YCu from first principles

The structural, electronic and elastic properties of YCu compound in the B2 (CsCl) phase were investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA). The electronic density of states (DOS) obtained in this way accorded well with the results of a recent study utilizing the full-potential linearized augmented plane wave (FLAPW) method. We also found that the density of d-states at the Fermi energy was low. The calculated equilibrium properties such as lattice constant, bulk modulus and its first derivative, and the elastic constants were in good agreement with experimental and theoretical results.

Electronic and phonon structures of AuGa2 and AuIn2

We have studied structural, electronic and dynamical properties of AuGa2 and AuIn2 by employing the plane-wave pseudopotential method within the density functional theory. The structural results are in good agreement with previous experimental and other theoretical results. The calculated electronic band structures for both materials have been compared with the angle-resolved photoemission spectroscopy experiment data along the [100] symmetry direction. Phonon dispersion curves and density of states were calculated by employing a density-functional perturbation theory. The calculated zone-centre optical phonon modes for these materials are in good agreement with experimental data.

Elastic and phonon properties of FeSi and CoSi in the B2 structure

First principles calculations of structural, electronic, elastic, and phonon properties of the intermetallic compounds FeSi and CoSi in the B2 (CsCl) structure are presented, using the pseudopotential plane-wave approach based on density functional theory, within the local density approximation. The optimized lattice constants, independent elastic constants, bulk modulus, and first-order pressure derivative of the bulk modulus are reported for the B2 structure and compared with earlier experimental and theoretical calculations. A linear-response approach to density functional theory is used to derive the phonon dispersion curves, and the vibrational partial and total density of states. Atomic displacement patterns for FeSi at the Γ, X, and R symmetry points are presented. The calculated zone-center optical phonon mode for FeSi is in good agreement with experimental and theoretical data.

First principles study of hydrogen storage material NaBH4 and LiAlH4 compounds: electronic structure and optical properties

A comprehensive study of structure, phase stability, optical and electronic properties of LiAlH4 and NaBH4 light-metal hydrides is presented. The calculations are carried out within density functional theory using the full potential linear augmented plane wave method. The exchange-correlation potential is treated within the local density approximation and the generalized gradient approximation (GGA) to calculate the total energy. Furthermore, the Engel–Vosko GGA approach is employed to compute electronic and optical properties such as reflectivity spectra. The phases α, β and γ of LiAlH4 and NaBH4 hydrides are investigated, the phase transition from the β to the high-pressure γ phase is determined for NaBH4 and is accompanied by a 1% volume decrease. For LiAlH4, no phase transition is detected. The materials under consideration are classified as wide band gap compounds. From the analysis of the structures at different phases, it is deduced that the hydrides show strong covalent interaction between B (Al) and H in the [BH4]− ([AlH4]−) anions and ionic bonding character between [BH4]− and Na+ for NaBH4, and [AlH4]− and Li+ for LiAlH4. The complex dielectric function, absorption coefficient and the reflectivity spectra are also computed and analyzed in different phases.

Ground state and phonon spectrum of NiSi2

We have studied structural, electronic, elastic and dynamical properties of NiSi2 by employing the plane wave pseudopotential method based on density functional theory within the local density approximation. The calculated lattice constant, bulk modulus and first-order pressure derivative of the bulk modulus are reported and compared with earlier available experimental and theoretical calculations. Numerical first-principles calculations of the elastic constants were used to calculate C11, C12 and C44 for NiSi2. The calculated electronic band structure has been compared with angle-resolved photoemission spectroscopy experimental data along the [100] and [111] symmetry directions. A linear response approach to density functional theory is used to derive the phonon dispersion curves and phonon partial density of states. Atomic displacement patterns for NiSi2 at the Γ, X and L symmetry points are also presented.

Investigation of electronic structure and thermodynamic properties of quaternary Li-containing chalcogenide diamond-like semiconductors

Using first-principles calculations based on density functional theory, the structural, electronic and thermodynamic properties of Li2CdGeS4 and Li2CdSnS4 compounds are investigated. We confirmed that both Li2CdGeS4 and Li2CdSnS4 are diamond-like semiconductors of the wurtz-stannite structure type based on that of diamond in terms of tetrahedra volume. All the tetrahedra are almost regular with major distortion from the ideal occurring in the LiS4 tetrahedron, with values for S-Li-S ranging from 105.69° to 112.84° in the Li2CdGeS4 compound. Furthermore, the Cd-S bond possesses a stronger covalent bonding strength than the Li/Ge-S bonds. In addition, the inter-distances in Li2CdSnS4 show a larger spread than the distances in the Li2CdGeS4 compound. The electronic structures have been calculated to understand the bonding mechanism in quaternary Li-containing chalcogenide diamond-like semiconductors. Our results show that Li2CdGeS4 and Li2CdSnS4 are semiconductors with a direct band gap of 2.79 and 2.42 eV and exhibit mixed ionic-covalent bonding. It is also noted that replacing Ge by Sn leads to a decrease in the band gap; this behavior is explained in terms of bond lengths and electronegativity differences between atoms. Optical properties, including the dielectric function, reflectivity, and absorption coefficient, each as a function of photon energy are calculated and show an optical anisotropy for Li2CdGeS4 and Li2CdSnS4. The static dielectric constant and static refractive index decrease when Ge is replaced by Sn. The influence of pressures and temperatures on the thermodynamic properties like the specific heat at constant volume and at constant pressure the Debye temperature the entropy and the Gruneisen parameter have been predicted at enlarged pressure and temperature ranges. The principal aspect from the obtained results is the close similarity of both compounds.