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The CoYSb (Y = Cr, Mo and W) compounds which are XYZ type half-Heusler alloys and also exist in the face centred cubic MgAgAs-type struc-ture conform to F ̄43m space group. In the present work, these compoundsare investigated in different atomic arrangements called, Type-I, Type-II andType-III phases, using Generalized Gradient Approximation (GGA) in the Density Functional Theory (DFT) implemented in QE (Quantum EspressoAb-Initio Simulation Package). The ferromagnetic state of these alloys is studied after investigating their stable structural phase. The calculated electronic band structure and the total electronic density of states indicated nearly half-metallic behaviour in CoMoSb with a possibility of being used in spintronic application, metallic in CoWSb and half-metallic in CoCrSb, with the minority spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behaviour of these alloys in the stable phase. Finally, due to its high Debye temperature value, CoCrSb possesses a stronger covalent bond than CoMoSb and CoWSb, respectively.

Electronic and optical properties of β-HgS have been investigated using the density functional theory. The calculated lattice parameter is 6.043 Å, the bulk modulus is 57.17 GPa, the equilibrium volume is 55.25 Å3. From the band structure, a direct band gap of 0.00002 eV was obtained, which agreed well with other calculations. The plot of the dielectric constant against photon energy indicated several distinctive peaks. The imaginary part has a peak value of 34.99 at 0.47 eV and the real part has a peak value of 29.65 at 0.40 eV. The values obtained for electronic and optical properties of β-HgS are essentially important for applications in optoelectronic

The quest for materials with optimum photovoltaic conversion efficiency leads to the discovery of CH3NH3PbI3, which has shown exciting improvement in power conversion efficiency over the silicon-based technology. This research uses PBEsol–KJPAW and PBE-NC functionals as implemented in Density Functional Theory to study the effects of Mg doping in CH3NH3PbxMg1–xI3 solar cell absorber for x = 0, 0.25, 0.50, 0.75, 1. The Absorption spectrum is computed with Time-Dependent Density Functional Perturbation Theory while the optical gap is calculated by fitting the absorption edge with the Tauc direct and indirect allowed transition. The ground state energy and lattice parameters of CH3NH3PbxMg1–xI3 in its cubic, tetragonal and orthorhombic crystal structures were calculated to determine its equilibrium structure, which appears to be simple cubic for all the compounds of interest. Electronic band gaps were calculated to be in the range 1.16–2.12 eV, suggesting an excellent power conversion efficiency according to the Shockley–Queisser efficiency limit, but the optical gaps extrapolated from the absorption spectrum is larger than the calculated DFT band gap, as a result of underestimation of calculated DFT band gap in Mg-doped CH3NH3PbI3. CH3NH3PbxMg1–xI3 is found to be brittle, moderately incompressible with Vickers hardness in the range of 6.776–9.153 GPa. The brittleness, incompressibility, and hardness all increase with Mg concentration. The amount of solar radiation absorbed and the percentage reflectivity depends on the concentration of Pb while transmitted solar irradiation increase with Mg concentration, these suggest that MAPbI3 may have better power conversion efficiency compared to Mg-doped MAPbI3, but Mg doping will reduce the toxic effect of Pb and produce much more power conversion efficiency than the silicon-based solar cell.

This study has examined the ground-state electronic, structural and, in addition, paramagnetic properties of semiconductor MgTe in its zinc blende phase by using the density functional theory (DFT). Exchange-correlation potentials have been approximated with the Projected Augmented Wave (PAW) Generalized Gradient Approximation (GGA). From the calculated lattice parameter, we determined the bulk modulus and first pressure derivative. Also, reported are other ground state properties: density of state (DOS), band structure, projected DOS (PDOS) and magnetic properties. A direct large band-gap of 2.358 eV was observed from the band structure that has close concurrence with former reported values. Although this value is also smaller than the reported experimental values, it is the closest of all the calculated values. The magnetic state of the compound was observed to be paramagnetic in the ground state.

This work examines the density functional theory calculation of the structural, electronics and optical properties of BxCo4-xSb12 alloys from the first principle calculation with quantum expresso via the generalized gradient approximation and Perdew-Burke-Ernzerhop exchange-correlation functional. The lattice parameter, electronic band structure, density of state and projected density of state are evaluated and the results are compared to the theoretical and experimental data available for Co4-xSb12. The electronic band structures revealed a direct band gap of 0.78 eV and 0.80 eV for Co4-xSb12 and FeCo3Sb12 respectively while AlCo3Sb12 shows an indirect band gap of 0.13 eV. However, the density of state has the maxima peaks at −1.84 eV, −1.23 eV and −1.37 eV for Co4Sb12, FeCo3Sb12 and AlCo3Sb12 in order. Based on the projected density of state analysis, electronic states are dominated by Co-3d orbital for both compounds. For optical properties, random-phase approximation technique is used. The implementation approach is based on a multi-particle scheme that gives high accuracy compared to simulations with single particle dielectric tensor. A stronger optical responses are observed between infrared and visible region (low energy region) which indicate the nanostructure of BxCo4-xSb12 alloys. The results obtained verify the effectiveness and efficiency of BxCo4-xSb12 compounds for wave guide, photonic circuit design and nanoelectronics applications.

An understanding of the complex index of refraction of Gallium Nitride (GaN) is important because of the increasing application of GaN in many high frequency, optical and electronics devices. Complex index of refraction of Gallium Nitride (GaN)have been investigated theoretically by means of Kramers and Kronig method in the photon energy range 2.0 – 10.0eV. We obtained refractive index which has a maximum value of 2.89 at photon energy 7.0eV, the extinction coefficient which has a maximum value of 1.17 at photon energy 7.0eV, the dielectric constant, the real part of the complex dielectric constant has a maximum value of 7.0 at photon energy 7.0eV and the imaginary part of the complex dielectric constant has a maximum value of 6.79 at photon energy 7.0eV, the transmittance which has a maximum value of 0.18 at photon energy 7.0eV, the absorption coefficient which has a maximum value of 86.18 at photon energy 7.0eV. The values obtained for complex index of refraction ofGaN are essentially important for emerging GaN applications such ashigh-power and high-frequency devices, solar cell arrays for satellites, communications and optoelectronics devices.

Electronic properties of PbTe in its Rock-Salt (B1) phase have been investigated using density functional theory (DFT) as well as the Phonon Band Structure of PbTe using density functional perturbation theory (DFPT). The lattice parameter, bulk modulus and pressure derivative are calculated as 6.608 A, 36.00 GPa and 3.39 respectively; The density of states (DOS) has a maximum peak of 3.2 states/eV at −3.00 eV, the spherical charge distributions between the Pb+2 and Te−2 ions depict that the system is an ionic compound; From the band structure, a direct band gap of 0.7968 eV was obtained which agreed well with other calculations. We observed a large splitting value of 2.16 THZ between the longitudinal optic (LO) and the transverse optic (TO) phonon branches along the Γ-point. The vibrational density of states (VDOS) has a maximum peak of 0.185 states/eV at 1.53 THZ. The values obtained for electronic properties and the phonon band structure PbTe are essentially important for PbTe energy applications such as thermoelectric, solar cells, biological imaging electroluminescent, infrared photodetectors and optoelectronic devices.

This work presents the report of density functional theory investigations into PdTiSn Half Heusler alloy using Boltzmann theory of BoltzTraP codes as incorporated in quantum ESPRESSO package with plane-wave pseudo-potentials to investigate the electronic band structure and transport properties of this compound. Also, transport effective mass and electronic fitness function for this system were computed from results of Boltzmann transport theory based calculations via transM code. A probe into the obtained band structure, classified PdTiSn as an indirect semiconductor with estimated band gap of 0.47 eV. This material possessed notable high conductivity values at carrier concentration (CC) of 1022 cm−3 in temperature range of 100–800 K. It was observed that within the investigated temperature range, for n- and p-types, there were sharp decreases in Seebeck coefficients, which later increased for the n-type. Power factors per relaxation time for both the n- and p-types increased as temperature increases with peak values recorded at 800 K beyond 1021 cm−3 CC and is higher for the p-type. The calculated electronic fitness function has a maximum value of 7 × 1020 W5/3m-s−1/3K−2, where the electron's and hole's concentrations are zero. This material also exhibited light effective mass, this responsible for its higher conductivity. The thermoelectric properties, effective mass and electron fitness function for pure PdTiSn half Heusler alloy are extensively reported here. The results of this study predict PdTiSn as a p-type semiconductor, which will provide better thermoelectric performance.

This study used first principles calculations within the generalized gradient approximation (GGA) via plane-wave pseudo-potential scheme to extensively study the magnetic, elastic, thermodynamic and thermoelectric properties of Co2TiAl and Co2VAl Heusler alloys at their optimized lattice constants. Elastic properties of these alloys were obtained by fitting the stress-strain relationship via Voigt-Reuss-Hill approximations. Thermodynamic properties were calculated within the implementation of thermo_pw package while thermoelectric properties were estimated from non-spin polarized calculations via Boltzmann semi-classical approach as implemented in BoltzTraP package at temperatures between 0 and 800 K. Calculations reaffirmed the stable electronic and magnetic states for the alloys to be half metallic ferromagnetic (HMF) states. The estimated band gaps in the minority spin channels were 0.431 and 0.399 eV for Co2TiAl and Co2VAl alloys respectively and these were justified by their corresponding density of states. The calculated magnetic moments for the respective alloys were 0.949 and 1.978 μB, which agreed with experimental, theoretical and Slater-Pauling rule determined magnetic moments. Elastic constants (C11, C12 and C44) obtained for these cubic systems fulfilled Born-Huang mechanical stability criteria, from which other elastic related quantities were extracted. Elastic calculations predicted these alloys to be metallic bonded, extremely incompressible, highly anisotropic and ductile in nature. Thermodynamic calculations showed that Debye vibrational energies, entropies and constant volume heat capacities of the alloys increased remarkably as temperature increased whereas vibrational free energies decreased steadily with increased temperature. Thermoelectric properties were also determined, with Co2TiAl having higher figure of merit (ZT) than Co2VAl within the investigative temperatures.

In this work, we report about the electronic and elastic properties of crystalline poly(3,4-ethylenedioxythiophene), known as PEDOT, in the crystalline form, studied in the framework of semilocal DFT, using the PBE and PBEsol exchange-correlation functional and PAW pseudopotentials. Contrary to previous molecular dynamics simulations, our calculations revealed that the most stable state structure of pristine PEDOT is monoclinic. We calculated the 13 independent elastic constants and the elastic compliance which enables us to establish other elastic properties of pristine PEDOT; the Pugh’s ratio and the Vicker’s hardness computed with PBE and PBEsol are in good agreement with each other. Finally, we compute the directional elastic modulii and found remarkable differences between different DFT functionals.

Many Heusler alloys have been discovered experimentally and theoretically, particularly, Co-based ones, owing to the growing attributes driven interests and suitabilities in spintronics. In this study, first principles calculations via generalized gradient approximations (GGA), with treatment of the electron-ion interactions using Kresse- Joubert Projected Augmented wave (KJPAW) pseudo-potentials were performed to comparatively and extensively investigate the effects of substituting Cr with Mn in Co2CrAl full Heusler alloy on their structural, magnetic, electronic, elastic, mechanical, thermodynamic and thermoelectric properties. Linear fitting of the stress-strain relationships of these cubic alloys at their respective optimized lattice parameters yielded three elastic constants, from which other mechanical parameters were obtained. Thermodynamic properties were determined from the Quasi-harmonic approximations in the framework of Debye model and non-spin polarized calculations as implemented in BoltzTraP code, gave thermoelectric properties in the temperature range of 0 and 800 K. Results obtained at ground states agreed reasonably with available data from experimental and theoretical investigations, and these revealed that the substitutive effects on these investigated properties were prominent in magnetic moments and half-metallicities, indicators of enhancements for spintronic applications and in thermoelectric figure of merits. These two alloys were ductile with metallic bonding systems and structurally, mechanically and thermodynamically stable in these investigative temperature ranges.

Here we report the electronic structure of praseodymium filled skutterudite compound PrOs4Sb12. The theoretical photoemission spectrum (PES) at ћω = 21.2 eV shows four distinct structures peaking at about -0.2, -7.7, -13.7 and -18.2 eV. But on increasing the photon energy to 40.8 eV, the peak at -0.2 eV becomes a prominent or pronounced peak, the peak at -7.7 eV decreases in intensity, the peak at -13.7 eV increases intensity, the peak at -18.2 eV reduces in intensity and another peak emerges. These structures are interpreted to be associated with the density-of-states features on the basis of the results of band structure calculation. Hence, the peak at -0.2 eV arises from the symmetry point P at -11.61 eV, the peak at -7.7 eV comes from the symmetry point P at -11.62 eV, the peak at -13.7 eV arises from the symmetry point P at -11.88 eV and the peak at -18.2 eV arises from the symmetry point P at -11.88 eV. The PES energy level difference for PrOs4Sb12 fell within the range -0.5 to -7.5 eV indicating that it can be used in designing electronic devices. The energies of specific electronic states in the band structure of PrOs4Sb12 showed that it could be used for the development of solid-state devices.

Detailed first-principle calculations of properties in zinc blende quaternary alloy [Formula: see text] at various concentrations are investigated using density functional theory (DFT) within virtual crystal approximation (VCA) implemented in alchemical mixing approximation. The calculated bandgaps show direct transitions at [Formula: see text]–[Formula: see text] and indirect transitions at [Formula: see text]–[Formula: see text], which are opened by increasing boron concentration. The density of state (DOS) revealed upper valence band (VB1) domination by [Formula: see text]-states atoms, while [Formula: see text]-states dominate the lower valence band (VB2); also, the DOS shows the contribution of [Formula: see text]-states to the conduction band. The first critical point in the dielectric constant ranges between 0.07–4.47 eV and is due to the first threshold optical transitions in the energy bandgap. Calculated static dielectric function (DF) [Formula: see text] is between 5.15 and 10.35, an indication that small energy bandgaps yield large static DFs. The present results indicate [Formula: see text]-[Formula: see text] alloys are suitable candidates of deep ultraviolet light emitting diodes (LEDs), laser diodes (LDs) and modern solar cell since the concentrations [Formula: see text] and [Formula: see text] make the bandgap and lattice constant of [Formula: see text]-[Formula: see text] quaternary alloys tunable to desirable values.

In the present study, ground state and elastic properties of semiconductor MgSe in zinc-blende phase are investigated using density functional theory (DFT). Exchange-correlation potentials are approximated with the generalized gradient approximation (GGA). From the calculated bulk modulus, we determine the refractive index, plasmon energy, cohesive energy and micro-hardness of the MgSe semiconductor binary alloy. The density of state (DOS), projected density of state (PDOS), phonon dispersion frequencies, charged density, electronic band structure and dielectric functions are also reported. From the band structure, a direct band gap of 2.50 eV was observed in close agreement with other reported calculations, but lower than the experimental value of 3.60 eV. Along the high symmetries directions, we found a striking resemblance between MgSe and a III–V semiconductor, while the high cohesive energy in MgSe suggests filled bonding orbitals which might result in decrease in atomic volume with corresponding increased compression of the s-orbitals under any transition series.

We have investigated the optical properties of gallium arsenide (GaAs) in the photon energy range 0.6–6.0 eV. We obtained a refractive index which has a maximum value of 5.0 at a photon energy of 3.1 eV; an extinction coefficient which has a maximum value of 4.2 at a photon energy of 5.0 eV; the dielectric constant, the real part of the complex dielectric constant has a maximum value of 24 at a photon energy of 2.8 eV and the imaginary part of the complex dielectric constant has a maximum value of 26.0 at a photon energy of 4.8 eV; the transmittance which has a maximum value of 0.22 at a photon energy of 4.0 eV; the absorption coefficient which has a maximum value of 0.22 × 108 m−1 at a photon energy of 4.8 eV, the reflectance which has a maximum value of 0.68 at 5.2eV; the reflection coefficient which has a maximum value of 0.82 at a photon energy of 5.2 eV; the real part of optical conductivity has a maximum value of 14.2 × 1015 at 4.8 eV and the imaginary part of the optical conductivity has a maximum value of 6.8 × 1015 at 5.0 eV. The values obtained for the optical properties of GaAs are in good agreement with other results.