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The aim of this paper is the prediction of the structural, electro-magnetic and mechanical properties of the Co2HfZ (Z = Al, Ga, Si and Sn) full Heusler compounds using a full-potential linearized augmented-plane wave method (FP-LAPW) based on the Wien2k program. For the structural and mechanical properties, we used the Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA) and modified Becke and Johnson (mBJ) schemes to compute the fundamental parameters. The latter was employed for the electro-magnetic properties, to calculate the band structures (BS) and density of states (DOS) of these compounds. Our results showed the half-metallicity of Co2HfZ (Z = Al, Ga, Si and Sn). The obtained energy revealed that these alloys were thermodynamically stable and could be hence elaborated experimentally. The mechanical properties indicated that our compounds were anisotropic ductile materials. Our findings greatly support that these compounds are highly attractive potential candidates for electro-spintronic applications.

In this paper, the topological phase of LuX (X = Sb, Bi) compounds under hydrostatic and biaxial pressures is investigated based on first principles of density functional theory by WIEN2k package. To find out the Z2 topological invariants of centrosymmetric compounds with the time reversal symmetry, the Bloch functions parity analysis can be used via electronic band structure calculations. So in this paper the Z2 topological invariants of the LuX (X = Sb, Bi) compounds with the time reversal and inversion symmetries are calculated using this approach. The results show that the d-p band inversion can be occurred in these compounds due to spin orbit interaction and appropriate pressure. These compounds have the strong electronic interaction due to their large d-electronic orbitals near the Fermi energy. The dynamic stability of these compounds is verified by phonon modes analysis. The surface states topological phase of these compounds are investigated based on the band structure calculations.

Carbon interstitial atoms, when dissolved in bcc Fe, induce elastic dipoles with tetragonal symmetry. Mechanical loss spectra indicate the presence of interstitial atoms by Snoek peaks. The magnitude of the peaks is proportional to the concentration of interstitial atoms in solution and the dipole strength. The ab initio computer simulation of lattice parameters and local structure distortions caused by the Fe–C system with three carbon atoms in different octahedral positions of one sublattice has been carried out using WIEN2k software. The simulation results allowed us to propose a way to estimate the dipole strength. The value found are λ1- λ2 = 0.58.

Complex study of the electronic structure of the Ag2HgSnSe4 compound employing both experimental and theoretical methods was carried out in the present work. In particular, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+ ion-irradiated surfaces of Ag2HgSnSe4 single crystal have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that Ag2HgSnSe4 single crystal surface is sensitive with respect to Ar+ ion-irradiation. Particularly, Ar+ ion bombardment of the single crystal surface causes significant modification in topmost surface layers resulting in abrupt decreasing the content of Hg atoms in the layers. The X-ray emission band representing the energy distribution of the Se 4p states was measured and compared with the XPS valence-band spectrum provided that a common energy scale is used. Results of such comparison reveal that the main contributions of the Se 4p states occur at the top and in the upper portion of the valence band. The experimental findings were confirmed by first-principles band-structure calculations performed in the present work employing the augmented plane wave+local orbitals (APW+lo) method as realized in the WIEN2k package. The calculations indicate that the Hg 5d and Ag 4d states are the principal contributors to the bottom and the central part of the Ag2HgSnSe4 valence band, respectively, while its upper part is dominated by contributions of the Se 4p states. Regarding the occupancy of the conduction band, the present APW+lo calculations manifest that its bottom is dominated by the unoccupied Sn 5s states. The principal optical characteristics of Ag2HgSnSe4 are elucidated by the calculations.

The ab-initio calculations and experimental investigations were performed for the study of Au incorporated MoS2 thin films. The electronic and optical properties were predicted using simulations with density functional theory based on Wien2k code. Perdew-Burke-Ernzerhof function under generalized gradient approximation was implemented for the exchange and correlation function. MoS2 and Au:MoS2 thin films were grown on Si substrates using magnetron sputtering deposition. Morphology and elemental composition analysis reveal the formation of uniform, smooth, and phase pure growth of thin films. A strong correlation in electronic and optical parameters was found in the outcomes of simulations and experimental study. The increase of optical absorption response in visible regime makes the Au incorporated MoS2 composition more favorable for photovoltaic applications.

This computational study is focused on the optical properties of Cu doped CdS for various supercell configurations. In this regard, Cd atoms are substituted by Cu atoms at various lattice positions and the results are almost similar except in the case of 2 × 2 × 2 supercell which involves more correlations and atomic interactions than those involved in other supercell configurations. Also by increasing the supercell size the optical properties are changed. The study has been performed by applying density functional theory in the Wien2K code using PBE-GGA approximations. The addition of Cu into CdS may be responsible for p-type character of CdS as illustrated by PDOS and TDOS calculations. The optical absorption increases in visible range but shows oscillatory trend in the UV region. However, doping of Cu into CdS lattice illustrates an enhancement in its electro-optical properties.

The structural, elastic, mechanical, optoelectronic, and thermodynamics properties of InP, InSb, and their mixed ternary alloys, InP1-xSbx, in their zinc blende structure for 0 ≤ x ≤ 1, are studied. The “full potential linearized augmented plane wave (FP-LAPW) method framed within density functional theory (DFT)" as realized in WIEN2k computational code is employed for all calculations. The results of elastic constants for simulated structures of InP1-xSbx alloys are the first time computed in this study. The results of the elastic constants showed that the InP1-xSbx alloys, for all compositions of x, are brittle and mechanically stable above and beyond showing the strong anisotropic character as well. On the other hand, the obtained results of InP1-xSbx for lattice parameters, bulk modulus, and band gap energy exhibit their nonlinear character. Also, the optical properties are determined at the level of the mBJ scheme for an energy range from 0 to 40eV. However, the “quasi-harmonic Debye model” is used to investigate the thermodynamics properties for example Debye temperature, specific heat, entropy, and their dependence on pressure, and the temperature is also analysed for the mentioned alloys. Our computed results for optical band gap and absorption coefficients expose these alloys as suitable candidate materials for optoelectronics applications in the infrared as well as in the visible region.

Strong relationship between direct X - X bonds and electronic properties in many thermoelectric materials is observed. In present work investigation on the relation between properties of such bonds in skutterudite-structured compounds and band gap size was performed. Various compositions of Co 1-x Rh x Sb 3 (x = 0 to 1) solid solutions were studied theoretically, using experimental structure data found in a literature as well as structures optimized through ab initio methods. Electronic structure of a set of pure CoSb 3 /RhSb 3 structures subjected to various external pressure conditions as well as solid solutions was obtained within DFT calculations using WIEN2k package. Topological properties of total electron density were determined under Bader's QTAiM formalism. Importance of charge transfer changes between Co/Rh and Sb atoms and their relation to the band structure were highlighted. According to presented results, strong influence of longer Sb-Sb bonds of Sb 4 ring on the band structure was explained, suggesting possible ways of CoSb 3 -RhSb 3 band gap engineering.

We have studied the structural, electronic, elastic, magnetic, thermal and thermodynamic properties of the quaternary Heusler alloys Cr2GdSi1−xGex (x = 0, 0.25, 0.5, 0.75, 1) with the linearized augmented plane wave method based on density functional theory and implemented in WIEN2K code. For exchange correlation potential, we have used the generalized gradient approximation (GGA) within the Perdew-Burke-Ernzerhof (PBE 96) parameterization. Our results provide a theoretical study for the mixed Heusler Cr2GdSi1−xGex (0

First-principles calculations are carried out to perform the structural properties using two dimensional search of equation of state (EOS), elastic constants and thermodynamic properties for zinc-blende (ZB) and wurtzite (WZ) phases of CdSexTe1−x alloys for all compositions x (x = 0, 0.25, 0.5, 0.75, 1). We have used the full-potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT), which has been implanted in the WIEN2k code, along with the improved generalized gradient approximation (PBE-GGA) to treat exchange-correlation functional. The mechanical and thermodynamic properties of CdSexTe1−x alloys are studied using the optimized lattice parameters from two dimensional search of EOS at zero pressure. The ZB and WZ phases of the ternary CdSexTe1−x alloys are found to be mechanically stable within PBE-GGA exchange-correlation over all the range of the Te concentrations (x = 0, 0.25, 0.5, 0.75, 1). We have found that the CdSe is mechanically the strongest material in the ternary CdSexTe1−x alloys. We concluded that the calculated values of Cauchy pressure and Poisson's ratio predict that the ionic bonds for both ZB and WZ phases of CdSexTe1−x ternary alloys are more dominant for all compositions of x(x = 0, 0.25, 0.5, 0.75, 1) within PBE-GGA exchange-correlation. Our results exhibit a non-linear relationship between elastic constants and Se concentrations. Moreover, the elastic properties of cubic (ZB) and hexagonal (WZ) phases of CdSexTe1−x alloys, including elastic constants, bulk and shear moduli are calculated and compared with available theoretical and experimental results, good agreement was found.

The structural stability, band structure, density of states (DOS), magnetic and mechanical properties of Co-based equiatomic quaternary Heusler alloys (EQHAs) CoYCrZ (Z = Si, Ge, Ga, Al) are examined by employing 1st principle calculations in the framework of density functional theory (DFT) as embedded in Wien2k code. The generalized gradient approximation (GGA) of Perdew-Burke Ernzehrof (PBE) is used for all these calculations. The lattice constants obtained by the optimization of structures and Type-II is found the most stable configuration for all alloys. The band diagrams and DOS calculations show that all these materials possess half metallic (HM) character because they have band gap in minority spin channel. The origin of band gap has been explained which is due to the robust d-d hybridization among transition metals (TMs). The obtained magnetic moments (MMs) are in accordance to the Slater-Pauling rule. The considered materials have high MMs and all alloys showed 100% spin polarization (SP). Curie temperature has also been calculated and reported for all these alloys. In order to check the mechanical stability, the calculations for elastic constants and other mechanical parameters are carried out which have revealed that all alloys are stable and have ductile nature. All the considered alloys in this study are reported for the first time and no data is available for comparison. It is envisaged these alloys are suitable for spintronic applications as in magnetic tunnel junctions (MTJs), spin valves, and spin injectors etc.

The topological band structures of InAsxSb1−x (x = 0, 0.25, 0.5, 0.75, 1) alloys have been investigated using density functional theory by utilizing the Wien2k package. These alloys are in a topologically trivial phase in their unstrained states and exhibit a small band gap. Since in small band-gap cubic semiconductors the nontrivial topological phase can be achieved by lattice expansion, we investigate the effect of hydrostatic and biaxial lattice expansion on band inversion strength and band order of these alloys. It is found that under reasonable hydrostatic lattice expansion, InAsxSb1−x (x = 0, 0.25, 0.75, 1) alloys with cubic symmetry and InAs0.5Sb0.5 alloy with tetragonal symmetry, are converted to nontrivial topological semiconductors with zero band gap and non-zero band gap, respectively. In order to convert InAsxSb1−x (x = 0, 0.25, 0.75, 1) alloys into topological semiconductors with non-zero band gap, we let the systems of InAsxSb1−x (x = 0, 0.25, 0.75, 1) alloys undergo a biaxial lattice expansion. Thus by breaking the cubic symmetry in these alloys, not only they are converted to topologically nontrivial phase but also a small band gap is opened at Γ point.

The theoretical calculations on structural, electronic, half-metallic and elastic properties of both VZrAs, VZrSb half-Heusler compounds and Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) diluted magnetic semiconductors (DMSs) have been investigated using WIEN2k. In Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs, the ferromagnetic phases are more stable than non-magnetic and antiferromagnetic phases. In VZr(As, Sb) compounds, the ferromagnetic (FM) phases in Type II structure are more stable energetically. The spin-up electrons of both half-Heusler compounds have semiconducting nature with 0.643 and 0.799 eV energy gaps while spin-down electrons of Al0.875Fe0.125As, Al0.9375Fe0.0625As and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs have semiconducting feature. The mechanically stability conditions are provided by all compounds except VZrAs half-Heusler compound. Therefore, VZrSb, Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) diluted magnetic semiconductors (DMS) are mechanically stable against the deformation. The VZrAs compound can be deformed in the experimental process since it does not provide the C-11 > C-12 mechanical stability condition. According to conditions of the ductility or brittleness of polycrystalline material, both VZrAs and VZrSb half-metal compounds are ductile materials while Al1-xFexAs and Al1-xCoxAs (x = 0.0625, 0.125, 0.25) DMSs are brittle. Finally, VZr(As, Sb), Al1-xCoxAs (x = 0.0625, 0.125, 0.25) and Al1-xFexAs (x = 0.0625, 0.125) compounds were obtained true half-metal ferromagnetic materials (HMF) within 4.00, 2.00 and 5.00 mu(B)/f.u. (C) 2019 Elsevier B.V. All rights reserved.

The structural, electronic and bonding properties of ThCr 2 Si 2 -type compounds, namely, CaTM 2 Pn 2 (TM = Ni, Pd; Pn = P, As) with space group I4/mmm (139) are obtained under compression by means of Full Potential – Linearized Augmented Plane Wave (FP – LAPW) method as implemented in WIEN2K code. The optimized lattice parameter, the positional z -parameter, Fermi energy, Density of States (DOSs) at Fermi Level, electronic specific heat coefficient and the distance between Ni(Pd)–P(As) and P(As)–P(As) atoms at equilibrium lattice configuration and under compressions are reported. Electron density plots, band structure plots and DOS are illustrated and compared. Different bonding characteristics are noted and compared. Our work predicts the possible range of bond lengths for the occurrence of covalent bonding between the pnictogens in these compounds. High pressure band structure calculations reveal the possibility of Electronic Topological Transition (ETT) in these compounds.

A new package for calculating lattice constants and equation of state for hexagonal and tetragonal structure is released. We call it as 2D-optimize. The new package is compatible with the highly accurate all-electron full-potential (linearized) augmented plane-wave plus local orbital [FP-(L)APW+lo] method implemented in WIEN2k code. This package is available with WIEN2k code. We have performed a convenient volume and c/a structure optimization by using 2D-optimize package. First, we find the best value of c/a and therefore the energy for each volume, and then for those volumes and energies the equation of state (EOS) will obtained, and after that the value of c/a calculates within optimal volume. We have done 1D and 2D search of EOS for MnAs and Mg within PBE functional and compared the results with experimental data, the results of 2D search for EOS are better than 1D search of EOS. The cell parameters and the bulk modulus of 20 hexagonal structure compounds were calculated using the new package and compared with the experimental data.

The topological band structures of LuPdBi x Sb 1− x (for x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1) alloys have been investigated using density functional theory by Wien2k package. The generalized gradient approximation (GGA) and Engel–Vosko generalized gradient approximation (GGA_EV) have been used to obtain accurate the band inversion strength and band order. The calculated results show that LuPdBi x Sb 1− x alloys for x ⩾ 0.25 in GGA and x ⩾ 0.375 in GGA_EV are candidates for three dimensional topological insulator or topological metal. Furthermore the effect of hydrostatic pressure on band inversion strength and band order of these alloys has been investigated.

A new package for calculating the elastic constants of orthorhombic structure is released. The package called ortho-elastic. The formalism of calculating the ortho-elastic constants is described in details. The package is compatible with the highly accurate all-electron full-potential (linearized) augmented plane-wave plus local orbital [FP-(L)APW+lo] method implemented in WIEN2k code. Several orthorhombic structure compounds were used to test the new package. We found that the calculated elastic constants using the new package show better agreement with the available experimental data than the previous theoretical results used different methods. In this package the second-order derivative E ″ ( e ) of polynomial fit E = E ( e ) of energy vs strains at zero strain ( e = 0 ) , used to calculate the orthorhombic elastic constants.

Single crystals of the new diamond-like semiconductor Ag 2 ZnSiS 4 have been synthesized using high-temperature, solid state synthesis at 800 °C. The compound crystallizes in the monoclinic, noncentrosymmetric space group Pn with a = 6.4052(1) A, b = 6.5484(1) A, c = 7.9340(1) A, β = 90.455(1)° and R 1 (for all data) = 2.42%. The electronic band structure and density of states were calculated using density functional theory (DFT) and the full potential linearized augmented plane wave (LAPW) method within the Wien2k program suite. The calculated band structure suggests that Ag 2 ZnSiS 4 is a direct band gap semiconductor with a calculated band gap of 1.88 eV at the Γ-point. The calculated density of states of Ag 2 ZnSiS 4 is compared with that of AgGaS 2 . The band gap of Ag 2 ZnSiS 4 was also determined experimentally as 3.28 eV via optical diffuse reflectance spectroscopy.

The electronic properties of ABAs 2 (A = Zn, Cd; B = Ge, Sn) compounds have been investigated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method with an aim to study the effect of changing local environment by substituting cation(s) with corresponding next group element in reference compound (ZnGeAs 2 ) on these properties. The exchange and correlation (XC) effects are taken into account by an orbital independent modified Becke–Johnson (mBJ) potential as coupled with Local Density Approximation (LDA) for these calculations. We predict a direct band gap in all these compounds and observe that the band gap decreases with the change of either one or both cations. The calculated band gaps are in better agreement with corresponding experimental ones as compared to other calculations. The electronic band structure is analyzed in terms of contributions from various electrons and the covalency of two bonds, Zn As and Ge As has been discussed with respect to substitutions.

The structural, electronic and optical properties of ZnX and CdX (X = Se, Te and S) are studied using density functional theory by the Wien2k package. The energy band gap, real and imaginary parts of the dielectric function, energy loss function, optical absorption coefficient and reflectivity spectra of these compounds are calculated. The Engel–Vosko approach improves the energy band gaps of ZnX and CdX compounds. The calculated optical parameters are in good agreement with available experimental results, particularly in the Engel–Vosko approach. Furthermore the effect of hydrostatic pressure on the energy band gap, the real and imaginary parts of the dielectric function of these compounds is studied. The first and second order pressure coefficient for the energy band gaps, the static dielectric function and the static reflectivity spectra are calculated.

We report first-principles calculations to analyze the In-composition effect on band gap width of Sc1−xInxN alloys in wurtzite structure for the compositions x = 0 , 0.25 , 0.5 , 0.75 , 1 . The calculations were performed in the framework of the density functional theory (DFT) using the full potential-linearized augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We used both Perdew–Burke–Ernzerhof (PBE) and Engel–Vosko (EV) functional of generalized gradient approximation (GGA) for the exchange-correlation potential. First, the lattice parameters with PBE functional were optimized. Subsequently, using PBE and EV functional, the band structure at equilibrium volume for each In-concentration was calculated. The gap bowing in wurtzite structure was obtained and analyzed. The calculated band structure with PBE and EV functional for all the compounds are similar, however a band gap wider with EV functional was obtained.

We have investigated the electronic and optical properties of ordered Be x Zn 1− x Se alloys using a 8-atom supercell for compositions x = 0.0 , 0.25 , 0.50 , 0.75 and 1.0. We report ‘ state-of-the-art ’ calculations within generalized gradient approximation (GGA) and Engel-Vosko’s corrected generalized gradient approximation (EVGGA) using the full potential linear augmented plane wave (FPLAPW) method as implemented in the WIEN2K code. To see the effect of disorder, alloys are also modeled following the special quasirandom structure (SQS) approach. The calculated lattice constants scale linearly with composition (Vegard’s law). Dielectric functions for different compositional alloys are calculated for 8-atom cubic supercell and chalcopyrite structure corresponding to [0 0 1] superlattice which show good qualitative agreement when compared with experiment. The calculated band gaps are fitted with a quadratic equation E g ( x ) = a x 2 + b x + c . We find that there is a direct to indirect band gap crossover at x = 0.53 compared with the measured value x = 0.46 . The position of critical points (CP’s) E 0 + Δ 0 , E 1 and E 2 show good agreement with the experimental data. The difference between the calculated band gap and measured band gap decreases with increasing concentration of Be. The valence band maxima and conduction band minima are dominated by Se-3p and Zn-4s/Be-2p states for x = 0.0 and 1.0, respectively.

Although there have been several theoretical efforts in the past to calculate both the best structure of H–H pairs in Y and the total energies as well as electronic structures, there exist no studies of the relation between hydrogen ordering and the shape of the Fermi surface. We use the FLAPW method, as implemented in the Wien2k code, focusing our research on the relation between chain ordering of H, the relaxation of internal coordinates and the electronic properties for hypothetical α -YH1/3 and α -YH2/3. In addition to the relaxed atomic positions in the cell, we obtain information on the negligible role of the H 1s state contribution near E F and the shape of the Fermi surface.

We present an ab initio density functional study of magnetic phase transitions in the YCo3H2 system. The augmented plane wave and local orbital method as employed in the WIEN2K code is used to predict the structure and electronic structure of this compound. Comparison is made with recent X-ray diffraction and magnetization studies. The calculations suggest that the YCo3H2 system is ferrimagnetic in character. Further, fixed spin moment calculations are used to predict and interpret magnetic phase transitions observed in externally applied magnetic fields.