G. Uğur

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.

Structural, elastic, electronic, phonon and thermal properties of Ir3Ta and Rh3Ta alloys

We have studied the structural, elastic, electronic, phonon and thermodynamic properties of Ir3Ta and Rh3Ta alloys, using ab initio calculations. For the L12 phase, we report the calculated lattice constants, bulk modulus and elastic constants, and these values are compared with previously published values. We also derive the elastic constants from the values of the slopes of the acoustic branches in the phonon dispersion curves. The band structures show that both materials are metallic. The phonon dispersion curves, and their corresponding total and projected densities of states, are obtained using a linear response in the framework of the density functional perturbation theory. The specific heat capacity at constant volume and different temperatures is calculated, and this aspect is discussed using the quasi-harmonic approximation.

Ab-initio study of the structural, electronic, elastic and vibrational properties of the intermetallic Pd3V and Pt3V alloys in the L12 phase

Pseudopotential plane-wave method based on density functional theory within the generalized gradient approximation for the exchange-correlation potential has been applied to study the structural, electronic, elastic and vibrational properties of the binary intermetallic Pd3V and Pt3V in the L12 phase. The optimized lattice constant, bulk modulus and its pressure derivative, independent single-crystal elastic constants and elastic wave velocities in three different directions are evaluated and compared with the available experimental and theoretical data. The polycrystalline elastic parameters, hardness coefficient, elastic anisotropy, Debye temperature are estimated. The electronic band structure, electronic total and partial densities of states, and total magnetic moment of the Pd3V and Pt3V alloys are computed and analyzed in comparison with the existing theoretical and experimental findings. Phonon-dispersion curves and their corresponding total and projected densities of states were obtained for the first time using a linear-response in the framework of the density functional perturbation theory.

Investigation of the structural, electronic, elastic and thermodynamic properties of Curium Monopnictides: An ab initio study

The structural, electronic, elastic and thermodynamic properties of Curium Monopnictides CmX (X = N, P, As, Sb and Bi) are investigated using first-principles calculations based on the density functional theory (DFT) and full potential linearized augmented plane wave (FP-LAPW) method under ambient condition and high pressure. The exchange-correlation term is treated using two approximations spin-polarized local density approximation (LSDA) and spin-polarized generalized gradient approximation generalized (GGA). The structural parameters such as the equilibrium lattice parameters, bulk modulus and the total energies are calculated in two phases: namely NaCl (B1) and CsCl (B2). The obtained results are compared with the previous theoretical and experimental results. A structural phase transition from B1 phase to B2 phase for Curium pnictides has been obtained. The highest transition pressure is 122 GPa for CmN and the lowest one is 10.0 GPa for CmBi compound. The electronic properties show that these materials exhibit half-metallic behavior in both phases. The magnetic moment is found to be around 7.0 μB. The mechanical properties of CmX (X = N, P, As, Sb and Bi) are predicted from the calculated elastic constants. Our calculated results are in good agreement with the theoretical results in literature. The effect of pressure and temperature on the thermodynamic properties like the cell volume, bulk modulus and the specific heats C𝜗 and CP, the entropy 𝒮 and the Gruneisen parameter γ have been foreseen at expanded pressure and temperature ranges.

First-principles study of structural, electronic, elastic and phonon properties of AB2O4(A = Ge,Si;B = Mg,Zn,Cd) spinel oxides

The structural, electronic, elastic and phonon properties of the cubic spinels AB2O4 (A = Ge, Si; B = Mg, Zn, Cd) compounds at zero pressure are investigated via density functional theory (DFT) using the Perdew–Burke–Ernzerhof (PBE) exchange–correlation functional. It has been shown that the predicted values of the structural parameters (a0 and u), bulk modulus (B), elastic constants (Cij), shear modulus G and B/G ratio are in good agreement with the previously reported results. The phonon dispersion curves of the AB2O4 (A = Ge, Si; B = Mg, Zn, Cd) are calculated for the first time using the direct method. The estimated phonon spectra indicate that GeMg2O4, GeZn2O4, GeCd2O4, SiMg2O4 and SiZn2O4 are dynamically stable in the cubic spinel structure.

The lattice dynamics of some type-I and type-II alloys

SummaryThe lattice dynamical calculations are performed on some type-I and type-II alloys by using the third-neighbor Clark-Gazis-Wallis (CGW) model. The theory is used to compute the phonon dispersion curves, the frequency spectra and the lattice specific heat of the studied alloys. The obtained results are in good agreement with the experimental findings, and better than those obtained using other models.

Three-body effect on the lattice dynamics of some fcc d-band metals

SummaryIn the present analysis, the interaction system of an fcc d-band metal is considered to be composed of two-body and three-body parts. We use a new three-body potential developed by Akgün and Uğur to deduce the contribution of many-body forces to the dynamical matrix of the fcc structure. Two- and three-body potentials are first used, as an application to investigate the dynamical behaviors of fcc d-band metals, Ni, Pd, Cu and Ag. The parameters defining the two- and three-body potentials for the metals are evaluated from knowledge of the equilibrium pair energies, bulk modulus and total cohesive energies of the metals, following a procedure given by Akgün and Uğur. In this scheme the input data is independent of phonon frequencies and elastic constants of the metals. Finally, the phonon frequencies of the metals along the principal symmetry directions are computed using the calculated radial, tangential and three-body force constants. The theoretical results are compared to experimental phonon dispersions. The agreement shows that the proposed potentials and crystal model provide a reasonable description of the lattice dynamics of fcc d-band metals.

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.