S. Bin-Omran

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.

FP-LMTO method to calculate the structural, thermodynamic and optoelectronic properties of SixGe1−xC alloys

The structural and electronic properties of the ternary SixGe1−xC alloys have been calculated using the full-potential linear muffin-tin-orbital (FP-LMTO) method based on density functional theory within both local density approximation (LDA) and generalised gradient approximation (GGA). The calculated equilibrium lattice constants and bulk moduli are compared with previous results. The concentration dependence of the electronic band structure and the direct and indirect band gaps are investigated. Using the approach of Zunger and co-workers, the microscopic origins of the band gap bowing are investigated also. Moreover, the refractive index and the optical dielectric constant for SixGe1−xC are studied. The thermodynamic stability of the alloys of interest is investigated by means of the miscibility. This is the first quantitative theoretical prediction to investigate the effective masses, optical and thermodynamic properties for SixGe1−xC alloy, and still awaits experimental confirmations.

Structural, electronic, optical and elastic properties of the complex K2PtCl6-structure hydrides ARuH6 (A = Mg, Ca, Sr and Ba): first-principles study

Abstract We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydrides A2RuH6 (A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of the A2RuH6 systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg2RuH6, Ca2RuH6, Sr2RuH6 and Ba2RuH6, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time.

An ab initio study of the structural, elastic, electronic and optical properties of the newly synthesized nitridoaluminate LiCaAlN2

The structural parameters, elastic constants, electronic structure and optical properties of the recently reported monoclinic quaternary nitridoaluminate LiCaAlN2 are investigated in detail using the ab initio plane-wave pseudopotential method within the generalized gradient approximation. The calculated equilibrium structural parameters are in excellent agreement with the experimental data, which validate the reliability of the applied theoretical method. The chemical and structural stabilities of LiCaAlN2 are confirmed by calculating the cohesion energy and enthalpy of formation. Chemical band stiffness is calculated to explain the pressure dependence of the lattice parameters. Through the band structure calculation, LiCaAlN2 is predicted to be an indirect band gap of 2.725 eV. The charge-carrier effective masses are estimated from the band structure dispersions. The frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for polarized incident light in a wide energy range. Optical spectra exhibit a noticeable anisotropy. Single-crystal and polycrystalline elastic constants and related properties, including isotropic sound velocities and Debye temperatures, are numerically estimated. The calculated elastic constants and elastic compliances are used to analyse and visualize the elastic anisotropy of LiCaAlN2. The calculated elastic constants demonstrate the mechanical stability and brittle behaviour of the considered material.

Structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr, Ba)

Abstract First-principles calculations were performed to investigate the structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr, Ba) using two complementary approaches based on density functional theory. The pseudopotential plane-wave method was used to explore the structural and elastic properties whereas the full-potential linearised augmented plane wave approach was used to study the structural, electronic, optical and thermoelectric properties. The calculated structural parameters are in good consistency with the corresponding measured ones. The single-crystal and polycrystalline elastic constants and related properties were examined in details. The electronic properties, including energy band dispersions, density of states and charge-carrier effective masses, were computed using Tran-Blaha modified Becke-Johnson functional for the exchange-correlation potential. It is found that both studied compounds are direct band gap semiconductors. Frequency-dependence of the linear optical functions were predicted for a wide photon energy range up to 15 eV. Charge carrier concentration and temperature dependences of the basic parameters of the thermoelectric properties were explored using the semi-classical Boltzmann transport model. Our calculations unveil that the studied compounds are characterised by a high thermopower for both carriers, especially the p-type conduction is more favourable.

Structural, elastic and thermodynamic properties of tetragonal and orthorhombic polymorphs of Sr2GeN2: an ab initio investigation

ABSTRACT The structural, elastic and thermodynamic properties of the α (tetragonal) and β (orthorhombic) polymorphs of the Sr2GeN2 compound have been examined in detail using ab initio density functional theory pseudopotential plane-wave calculations. Apart the structural properties at the ambient conditions, all present reported results are predicted for the first time. The calculated equilibrium lattice parameters and inter-atomic bond-lengths of the considered polymorphs are in good agreement with the available experimental data. It is found that α-Sr2GeN2 is energetically more stable than β-Sr2GeN2. The two examined polymorphs are very similar in their crystal structures and have almost identical local environments. The single-crystal and polycrystalline elastic parameters and related properties – including elastic constants, bulk, shear and Young’s moduli, Poisson’s ratio, anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature – have been predicted. Temperature and pressure dependence of some macroscopic properties – including the unit-cell volume, bulk modulus, volume thermal expansion coefficient, heat capacity and Debye temperature – have been evaluated using ab initio calculations combined with the quasi-harmonic Debye model.

Structural, elastic, and thermodynamic properties under pressure of the FeC in the martensitic phase: an ab-initio study

A detailed theoretical study of structural, elastic, and thermodynamic properties of the FeC in the martensitic phase has been carried out using ab-initio calculations based on the density functional theory within the generalized gradient approximation. The optimized structural properties, the lattice constant and bulk modulus and its pressure derivative, have been evaluated. The single-crystal elastic constants as well as the polycrystalline elastic moduli and their related properties have been calculated using the efficient strain–stress method, and the relevant mechanical properties of the FeC in the martensitic phase have been discussed. Pressure and temperature dependence of the lattice constant, bulk modulus, thermal expansion coefficient, heat capacity, Debye temperature, and Grüneisen parameter of the FeC in the martensitic phase have been investigated using the quasi-harmonic Debye model.

Hydrostatic pressure effects on the structural, elastic and thermodynamic properties of the complex transition metal hydrides A2OsH6 (A = Mg, Ca, Sr and Ba)

ABSTRACT We report a systematic first-principles density functional theory study on the pressure dependence of the structural parameters, elastic constants and related properties and thermodynamic properties of the complex transition metal hydrides Mg2OsH6, Ca2OsH6, Sr2OsH6 and Ba2OsH6. The calculated structural parameters are in excellent agreement with the existing data in the scientific literature. The single-crystal elastic constants and related properties were predicted using the stress–strain method. The elastic moduli of the polycrystalline aggregates were evaluated via the Voigt–Reuss–Hill approach. The dependences of the lattice parameter, bulk modulus, volume thermal expansion coefficient, isobaric and isochoric heat capacity and Debye temperature on the pressure and temperature, ranging from 0 to 15 GPa and from 0 to 1000 K, respectively, were investigated using the quasi-harmonic Debye model in combination with first-principles calculations.