WIEN2k Code Research Articles

An Examination of the Vibrational, Mechanical, Thermoelectric Features and Stability of Novel Half‐Heusler XVIn (X = Pd, Pt) by Density Functional Theory Computation

Modern manufacturing is primarily focused on providing things that are accessible, environmentally conscious, and energy efficient. An effort has been made herein to investigate the compounds that meet these requirements. The full‐potential linearized augmented plane wave method, in Wien2k code, is used to examine the structural, vibrational, mechanical, and transport properties of XVIn (X = Pd, Pt) half‐Heusler compounds. The generalized gradient approximation is used for structural optimization. The computed lattice constants are consistent with earlier theoretical and experimental results. The XVIn (X = Pd, Pt) investigation reveals that the material is inherently ductile and mechanically stable. It is found that XVIn (X = Pd, Pt) has a direct bandgap and a semiconducting property. The modified Becke–Johnson exchange approximation yields bandgap magnitudes of 0.25 and 0.55 eV for PdVIn and PtVIn, respectively. The Boltzmann transport offered by the BoltzTrap software is used to explore thermoelectric characteristics. The values of figure of merit (ZT) obtained for XVIn (X = Pd, Pt) compounds are very close to unity in the chemical potential range from −0.15 to 0.15 eV, indicating that they can be used to make thermoelectric devices with the maximum possible efficiency.

First principle study of structural, electronic, optical, and thermoelectric properties of Zr1-x MxNiSn (M = Ta, Nb and x = 0.25, 0.5, 0.75) half Heusler compounds: Green energy applications

In the present paper, the physical properties of doped Zr1-x MxNiSn (M = Ta, Nb and x = 0.25, 0.5, 0.75) half Heusler compound were investigated using density functional theory (DFT) with GGA-PBE and Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potentials. The Full Potential Linearized Augmented Plane Wave (FP-LAPW) technique was used as incorporated in the WIEN2k code. The band structures, as well as the density of states (DOS), are also studied. The lattice constants of 6.15 Å for pure and 6.12 Å reinforced compounds are obtained. The results show that pure alloys are semiconducting, and doped alloys are metallic. The elastic properties were also examined, and the results indicate that the compounds are mechanically stable. The optical properties such as absorption coefficient (I), optical conductivity (σ), electron energy-loss (L), refractive index (n), and extinction coefficient (K) were determined using the dielectric constants (ε). The optical results revealed that the materials are potential candidates for optoelectronic energy applications. The transport properties were also studied. The doping of Ta and Nb in ZrNiSn alloy increases the electrical conductivity in both GGA-PBE and TB-mBJ approaches. The electrical conductivity for pure ZrNiSn at room temperature is 4.67 × 1018 Ω−1m−1s−1 and it increases to 4.34 × 1020 Ω−1m−1s−1 for Zr0.5Ta0.5NiSn in GGA-PBE approach. The thermal conductivity's electrical component is increased by substituting Ta and Nb in the pure compound. The optical and thermoelectric properties make the materials a suitable candidate for green energy applications.

Investigations on the electronic, optical, thermoelectric and thermodynamic properties of quaternary coinage metal HgSeBr: a DFT study

In the present study, we examine the structural, electronic, optical, thermodynamic, and transport properties of CuHgSeBr, a mercury chalcogenide halide of coinage metals. Employing the FP-LAPW method via first principles calculations in the WIEN2k code, we investigate various properties including band structure, density of states, lattice constants, Debye temperature, and effective mass. CuHgSeBr manifests as an indirect bandgap semiconductor with a measure of 0.808 eV. Optical assessments using dielectric constants reveal its pronounced absorption of photons in the ultraviolet spectrum according to the ε 2 spectra. Furthermore, we present findings on electronic and lattice thermal conductivity, binding energy, and figure of merit. Notably, our calculations indicate a figure of merit of 0.226 at 300 K and 0.556 at 800 K, indicating CuHgSeBr’s potential as a valuable material for thermoelectric devices within industrial applications. Importantly, these detailed properties of CuHgSeBr have not been previously documented, underscoring the significance of this comprehensive research, which could guide future theoretical explorations aimed at identifying alternative materials with similarly intriguing properties.

Predictive analysis of a new FeVTe alloy from first principles: An excellent choice for thermoelectric applications

To predict the thermoelectric (TE), magnetic, and electrical properties of the novel half-Heusler FeVTe as well as its dynamical, mechanical, and structural stability, this investigation makes use of the WIEN2K code and the FP-LAPW technique, which relies on density functional theory (DFT). The exchange-correlation potential in this analysis is handled using the GGA-PBE approximation. According to our predicted results, we can draw the conclusion that this compound exhibits stability in the ferromagnetic (FM) type I phase and reveals a total magnetic moment of unity. From the computed band structure, FeVTe unveils half-metallic (HM) behaviour, showing metallic features in the spin-up direction and a semiconductor character in the downspin direction with an indirect bandgap of 1.27 eV. The alloy complies with the Slater-Pauling law based on the predicted spin-polarized magnetic moments (MMs). Also, the results obtained for the elastic constants suggest that this material is ductile, anisotropic, and mechanically stable. Moreover, this compound demonstrates a remarkable figure of merit at room temperature and elevated temperatures, suggesting its potential as promising material for thermoelectric applications.

Exploring the optoelectronic attributes, thermoelectric and photocatalytic potential of double perovskites Cs2BB'H6 (B = Al, Na and B'=Tl, In): A DFT study

Double perovskites Cs2BB'H6 (B = Al, Na and B'=Tl, In) have been scrutinized by employing density functional theory to calculate their electronic structures, thermodynamic stability, elastic, optical, thermoelectric and photocatalytic properties. The FP-LAPW is utilized in the WIEN2k code for the calculations. Exchange correlation potentials such as modified Becke-Johnson with the addition of spin-orbital coupling are employed. The positive phonon frequencies, negative formation energies and optimization curves of the structures endorse the complete stability of studied perovskites. Mechanical properties also provide evidence of the structure's stability. Both compounds exhibit a semiconductor nature with an indirect bandgap of 2.38 eV and 2.51 eV for Cs2AlTlH6 and 3.34 eV and 3.40 eV for Cs2NaInH6 with mBJ and mBJ+SOC potentials, respectively. The partial and total densities of states have been computed to investigate the orbital’s contribution. Calculations for optical response show the lowest energy loss and highest absorption in the ultraviolet range validating their use in optoelectronic devices. In addition, the evaluated thermoelectric response reveals their strong potential to use in renewable energy applications. Photocatalytic properties show the excellent response of both compounds for solar hydrogen synthesis.

The germanides ScTGe2 (T = Fe, Co, Ru, Rh) – crystal chemistry, 45Sc solid-state NMR and 57Fe Mössbauer spectroscopy

Abstract The TiMnSi2-type (space group Pbam) germanides ScTGe2 (T = Fe, Co, Ru, Rh) were synthesized from the elements by arc-melting. Single crystals were grown by annealing sequences of the arc-melted buttons in an induction furnace. The structures of ScFeGe2, ScRuGe2 and ScRhGe2 were refined from single-crystal X-ray diffraction data. In ScRuGe2, the ruthenium atoms have distorted octahedral germanium coordination (242–268 pm Ru–Ge). Three trans-face-sharing octahedra form a sub-unit which is condensed via common edges in c direction and connected via common corners with four adjacent blocks, forming a three-dimensional [RuGe2 type] substructure. The two crystallographically independent scandium sites have coordination numbers 15 (Sc1@Ge8Ru4Sc3) and 17 (Sc2@Ge7Ru6Sc4). Electronic band structure calculations for ScCoGe2 and ScRuGe2 show a net charge transfer from the scandium to the transition metal and germanium atoms, leading to a description with polyanionic networks Sc δ+[TGe2]δ−. The two crystallographically independent Sc sites are easily distinguishable by 45Sc magic-angle spinning (MAS)-NMR spectroscopy. Isotropic chemical shift values and nuclear electric quadrupolar interaction parameters were deduced from an analysis of the triple-quantum (TQ)-MAS NMR spectra. The electric field gradient parameters deduced from these experiments are in good agreement with quantum-chemical calculations using the Wien2k code. Likewise, the two crystallographically independent iron sites in ScFeGe2 could be discriminated in the 57Fe Mößbauer spectra through their isomer shifts and quadrupole splitting parameters: δ = 0.369(1) mm s−1 and ∆E Q = 0.232(2) mm s−1 for Fe1 and δ = 0.375(2) mm s−1 and ∆E Q = 0.435(4) mm s−1 for Fe2 (data at T = 78 K).

Density functional study of electrode material for magnetic tunnel junction designed using Co2TiZ (Z = Ge, Si) Heusler alloys

Some of the important applications in the field of spintronics are spin current driven logic devices having logic gates and in read heads in the hard disk drives, magnetic random access memory (MRAM) containing non-volatile memory units and extremely complex magnetic sensor. In spintronic applications, a magnetic tunnel junction (MTJ) is considered the back bone of all such devices. With this motivation, in present study we have predicted very low resistance area (RA) product value and high tunnel magneto resistance (TMR) of two designed MTJs by using full Heusler alloys (FHA) Co2TiZ (Z = Ge, Si) as electrode and MgO as barrier layer. These used half metallic (HM) Heusler alloys (HA), have been investigated using Wien2K code, via primary standard calculations and studied electronic and magnetic properties followed by structural and magnetic phase stability. Spin based band structure along with density of state (DOS) profiles are determined by considering both generalized gradient approximation (GGA) + modified Becke–Johnson functional (mBJ) functional and GGA potentials. For the estimation of the Curie temperature (Tc) mean field approximation (MFA) was considered. After determining physical properties of considered FHAs, spin polarised transport properties are calculated by using PWCOND code embedded in Quantum ESPRESSO (QE) for designed MTJs and obtained extremely low resistance-area product (RA) product and a high value of TMR which is found very suitable for spintronic device applications.

Thermodynamic, mechanical stability, and magneto-electronic features of Ti2-based quaternary Heusler alloys Ti2CoGa1−xCux (x=0, 0.25, 0.5, 0.75, and 1): A DFT investigation

In this work, we have used the full-potential linearized augmented plane wave (FP-LAPW) method implemented in the WIEN2k code combined with the generalized gradient approximation (GGA) of the density functional theory (DFT) to study the structural, elastic, mechanical, electronic, magnetic, and thermodynamic properties of the parent ternary inverse Heusler compounds based on Titanium and Cobalt Ti2CoGa, Ti2CoCu in the Hg2CuTi-type structure and their quaternary alloys Ti2CoGa[Formula: see text]Cux ([Formula: see text], 0.5, 0.75) for the chosen concentrations using a supercell with 16 atoms. We have calculated the structural properties, such as the lattice parameters, bulk modulus, and its first derivative, which are in good agreement with those that have been obtained based on other published theoretical methods. Also, we calculated the elastic constants of the studied Heusler alloys, and we found that these materials are elastically stable, ductile, and anisotropic. Therefore, the electronic and magnetic properties indicate that Ti2CoGa exhibits a half-metallic (HM) ferromagnetic behavior, while Ti2CoCu shows a metal and a non-magnetic (NM) character. Their quaternary alloys are found to be nearly HM ferromagnetic materials, with a magnetic moment mainly due to the atom Ti. Furthermore, the quasi-harmonic Debye model, which incorporates the lattice vibrations, was used to estimate the thermodynamic effects on some macroproperties of the Ti2CoGa[Formula: see text]Cux alloys. Successful results were achieved for the variations of the primitive cell volume, bulk modulus, heat capacities, and Debye temperature with pressure and temperature, respectively, in the ranges of 0–30[Formula: see text]GPa and 0–1400[Formula: see text]K. To our knowledge, no analogous investigations on the mechanical and thermodynamic properties of the Ti2CoGa[Formula: see text]Cux ([Formula: see text], 0.5 and 0.75) alloys have been performed to date. As a result, it is predicted that Ti2CoGa[Formula: see text]Cux Heusler alloys will be promising candidates for actual applications in spintronic devices.

First principle studies on structural, electronic, elastic, optical, and thermoelectric properties of XGeCl3 (X = Rb/Cs): Promising compounds for green energy application

AbstractThis study employed density functional theory (DFT) embedded in Wien2K code to evaluate the physical features of the XGeCl3 (X = Rb/Cs) cubic halide perovskites. The structural optimization has been performed considering generalized gradient approximation (GGA) and electronic properties have been computed considering modified Becke‐Johnson potential (mBJ). The formation energy and phonon dispersion analysis establish the stability of the investigated compounds. Mechanical stability is further confirmed by the computed diverse elastic coefficients. It has been discovered that the examined substances are naturally ductile. The refractive index, reflectivity, and absorption coefficient, are among the optical parameters that have been estimated and analyzed. Interesting results have been obtained for the transport properties of XGeCl3 (X = Rb/Cs). The XGeCl3 (X = Rb/Cs) exhibits a high Seebeck coefficient (X = Rb/Cs) and the largest figure of merit (about 0.99), indicating significant potential for thermoelectric applications.

Prediction of new MAX phase Zr2MSiC2 (M = Ti, V) compounds as a promising candidate for future engineering: DFT calculations

The Wien2K code, which utilizes density functional theory (DFT) first-principles method, is employed to examine the physical features of MAX phase Zr2MSiC2 (M = Ti or V). Furthermore, this method is also used to determine the Debye temperature and Vickers hardness of the compound. The computed structural parameters are highly realistic. Calculation of the formation energy, elastic constants Cij, and phonon band structure has confirmed with certainty compounds are thermodynamically, and mechanically stable. On the other hand, both Poisson's and Pugh's ratios reveal the compound's brittleness. The substance exhibits considerable elastic anisotropy. According to the electronic structure, our compounds contain a combination of ionic and metallic bonding. The melting temperature, Debye temperature, and minimum thermal conductivity confirm their use in harsh environments and as thermal barrier coatings. The fact that the rate of increase in Cv and the thermal expansion coefficient is the same in both compounds under varying pressure and temperature conditions suggests that they possess similar properties. The results that are being reported here increase the possible application of Zr2MSiC2 for future engineering.

Impact of samarium on magnetic and optoelectronic properties of magnesium-based MgSm2X4 (X = S and Se) spinels for spintronics.

Investigating novel compounds has become necessary due to the need for sophisticated materials in optoelectronic devices and spintronics. Because of their unique properties, magnesium-based spinels MgSm2X4 (X = S and Se) are very promising for these applications. We used the spin-polarized PBEsol for structural properties and the PBEsol functional for mechanical behavior, both using the WIEN2k code. Both compounds' stability in the magnetic and non-magnetic phases was validated by the Birch-Murnaghan equation of state, and their stability in the cubic phase was verified by the Born stability criterion. Their ductile character was shown by the computation of Pugh's ratio and Poisson ratio. Both MgSm2S4 and MgSm2Se4 display metallic behavior in the spin-up channel and semiconducting behavior in the spin-down channel, indicating a half-metallic nature, according to TB-mBJ potential calculations. With total magnetic moments of 20 μB, both materials showed ferromagnetic properties. Samarium ions contributed 5.27 μB for MgSm2S4 and 5.34 μB for MgSm2Se4. Furthermore, we computed optical parameters in the energy range of 0 to 15 eV, such as absorption, extinction coefficient, reflectivity, dielectric function, and refractive index. Our results demonstrate the potential of MgSm2X4 spinels for future technological developments by revealing their prospective optoelectronic and spintronic applications.

A computational study of the structural and thermal conduct of MgCrH3 and MgFeH3 perovskite-type hydrides: FP-LAPW and BoltzTraP insight

The structural and thermal conduct of MgCrH3 and MgFeH3 perovskite have been investigated using the full-potential linearized augmented plane wave (FPLAPW) method and the BoltzTraP package, implemented in the Wien2k code. The calculations involved fitting the Murnaghan equation of state to the calculated total energy and atomic volume. The present analysis includes key groundstate parameters, such as the lattice parameter and its pressure derivative. Where the electrical conductivity of MgTMH3 (TM=Cr and Fe), the thermal conductivity, merit factor, and power factor were discussed in the range of 300-900 K. The obtained outcomes exhibit interesting results to make these compounds as promising materials for thermoelectrical applications.

Study of half-metallic ferromagnetism and transport characteristics of double perovskites Sr2AIrO6 (A = Y, Lu, Sc) for spintronic applications.

The precise manipulation of electromagnetic and thermoelectric characteristics in the miniaturization of electronic devices offers a promising foundation for practical applications in quantum computing. Double perovskites characterized by stability, non-toxicity, and spin polarization, have emerged as appealing candidates for spintronic applications. This study explores the theoretical elucidation of the influence of iridium's 5d electrons on the magnetic characteristics of Sr2AIrO6 (A = Y, Lu, Sc) with WIEN2k code. The determined formation energies confirm the thermodynamic stability while an analysis of band structure and the density of states (DOS) reveals a half-metallic ferromagnetic character. This characteristic is comprehensible through the analysis of exchange constants and exchange energies. The current analysis suggests that crystal field effects, a fundamental hybridization process and exchange energies contribute to the emergence of ferromagnetism due to electron-spin interactions. Finally, assessments of electrical and thermal conductivities, Seebeck coefficient, power factor, figure of merit and magnetic susceptibility are conducted to assess the potential of the investigated materials for the applications in thermoelectric devices.

Ab initio study of the structural, electronic, and optical properties of MgTiO3 perovskite materials doped with N and P

This study investigates the electronic, optical, and structural properties of MgTiO3 perovskite materials, whether pure or doped with elements such as nitrogen (N) and phosphorus (P). The investigation utilizes density functional theory (DFT) with the GGA-mBJ approximation as implemented in the Wien2k code. The results show that the band gap energy of doped MgTiO3 is significantly lower than that of pure MgTiO3, which has a band gap of 2.933 eV, at oxygen sites with Y (N, and P). In particular, with N and P, the band gaps drop to 1.74 and 0.65 eV moreover, the Fermi energy (Ef) level shifts towards the valence band (VB) in a p-type semiconductor (SC). Further, we have analyzed the optical characteristics of these systems, including their dielectric function (ε1 and ε2), optical conductivity (σ), absorption coefficient (α), and refractive index (n). Furthermore, doping with N and P increases absorption in the visible spectrum, which raises the photocatalytic activity in the presence of light because the doped materials’ valence and conduction bands transition more readily, producing hydrogen. The discoveries above suggest that these materials possess a broad spectrum of applications, encompassing the creation of optoelectronic apparatus.

FIRST-PRINCIPLES CALCULATION OF STRUCTURAL, ELECTRONIC, AND OPTICAL PROPERTIES OF InP1-XSbX USING WC-mBJ FOR NANOSCALE IR APPLICATIONS

The structural, electronic, and optical characteristics of cubic InP<sub>1-x</sub>Sb<sub>x</sub>(x = 0, 0.25, 0.50, 0.75, 1) ternary alloys were explored using the full-potential linearized augmented plane wave density functional theory approach. The total energy vs. volume optimization, lattice constants, and density of states were investigated for InP<sub>1-x</sub>Sb<sub>x</sub> alloys using exchange correlation function Wu-Cohen generalized gradient approximation (WC-GGA), available with the WIEN2k code. Band structure of the alloys was calculated using TB-mBJ functional to achieve a higher bandgap accuracy. The results of the mBJ experiment are in close agreement to those of the other experimental studies when compared to WC-GGA. Dielectric function and energy loss function were calculated in order to explore optical properties of the alloys. It was noticed that the estimated lattice parameters exhibit reduction when the Sb content is increased. Furthermore, the compositional dependency of the structural, electronic, and optical properties were also reported. For the InP<sub>1-x</sub>Sb<sub>x</sub> alloys, a band gap of less than 1.6 eVwere observed, making it suitable for usage in infrared optoelectronics devices.

Investigation of half metallic properties of Tl2Mo(Cl/Br)6 double perovskites for spintronic devices.

The manipulation of electronic device characteristics through electron spin represents a burgeoning frontier in technological advancement. Investigation of magnetic and transport attributes of the Tl2Mo(Cl/Br)6 double perovskite was performed using Wien2k and BoltzTraP code. When the energy states between ferromagnetic and antiferromagnetic conditions are compared, it is evident that the ferromagnetic state exhibits lower energy levels. Overcoming stability challenges within the ferromagnetic state is achieved through the manipulation of negative ΔHf within the cubic state. The analysis of the half metallicity character involves an analysis of band structure (BS) and DOS, elucidating its mechanism through PDOS using double exchange model p-d hybridization. The verification of 100% spin polarization is confirmed through factors such as spin polarization and the integer value of the total magnetic moment. Furthermore, the thermoelectric response, as indicated by the ratios of thermal-electrical conductivity and ZT, underscores the promising applications of these compounds in thermoelectric device applications.

First-principles calculations to investigate the structural, electronic, optical, mechanical, and thermodynamic properties of double perovskites Ba2WB′O6 (B′ = Co, Fe, Mn, Ni, and Zn)

We utilized the WIEN2K code within the DFT framework to comprehensively investigate Ba2WBˈO6 (Bˈ = Mn, Fe, Co, Ni, Zn) double perovskite compounds. Structural stability, assessed by Goldsmith's tolerance factor (tG), revealed values close to unity, indicative of stable cubic perovskite structures. The Birch-Murnaghan's equation of state optimization determined ground states, unveiling trends in lattice constant (a0) and bulk modulus (B) for different cations. Structural and phonon stability were confirmed by negative energy formation and real frequencies in phonon calculations. DFPT results affirmed the thermodynamic stability of all compounds. Electronic band structure calculations identified Ba2WMnO6 and Ba2WNiO6 as conductors, while Ba2WCoO6 and Ba2WZnO6 were insulators with 3.7 eV and 3.8 eV band gaps, respectively. Ba2WFeO6 demonstrated semiconducting properties with a 2.37 eV band gap. Density of States (DOS) analysis supported the electronic band structure. Optical conductivity analysis revealed increasing values at higher energy ranges, followed by gradual decreases, differing between conductors and insulators. Absorption coefficient indicated potential suitability for optoelectronic devices, and refractive index analysis highlighted trends in material transparency. To understand fundamental properties, thermodynamic characteristics (thermal expansion coefficient, heat capacities, Debye temperature) were analyzed across a wide pressure (0–30 GPa) and temperature (0–1600 K) range.

Structural, optoelectronic, thermal and transport properties of hybrid perovskite (EAGeCl3) material

Hybrid halide perovskites are emerging as an encouraging option for the fabrication of solar systems. Ethyl-ammonium-based hybrid halide perovskites offer amazing qualities such as reduced bandgap, increased structure stability, and less toxicity. Properties like structural; electrical; optical; and thermoelectric of the material ethyl ammonium germanium chloride are calculated using density functional theory (DFT) simulation code WIEN2K and calculated the optimized structure; density of states; and band structure of EAGeCl3 using exchange-correlation potential KTB-mBJ, establishing it as a direct bandgap semiconductor. Several optical properties such as dielectric function; absorption coefficient; and refractive index over a photon energy spectrum over the range of 0 to 7 eV have also been calculated. In addition, transport coefficients also calculated dependent on concentration of charge carriers, the chemical potential, and temperature at which the material is operating. The findings emphasize the extraordinary properties of EAGeCl3, which has a high ability to absorb electromagnetic radiation, such as light, with a high efficiency, superior compound’s ability to generate an electric potential in response to temperature, among additional benefits. These discoveries confirm its suitability as an affordable material for use in photovoltaic devices, contributing to the resolution of environmental concerns.

Structural Analysis, Characterization, and First-Principles Calculations of Bismuth Tellurium Oxides, Bi6Te2O15

A single crystal of Bi6Te2O15 was obtained from the melt of the solid-state reaction of Bi2O3 and TeO3. Bi6Te2O15 crystallizes in the Pnma space group (No. 62) and exhibits a three-dimensional network structure with a =10.5831(12) Å, b = 22.694(3) Å, c = 5.3843(6) Å, α = β = γ = 90°, V = 1293.2(3) Å3, and Z = 4. The structure was determined using single-crystal X-ray diffraction. An asymmetric unit in the unit cell, Bi3Te1O7.5, uniquely composed of four Bi3+ sites, one Te6+ site, and nine O2− sites, was solved and refined. As a bulk phase, Bi6Te2O15 was also synthesized and characterized using powder X-ray diffraction (XRD), infrared (FT-IR) spectrometry, and the thermogravimetric analysis (TGA) method. Through bond valence sum (BVS) calculations from the single crystal structure, Bi and Te cations have +3 and +6 oxidation numbers, respectively. Each Bi3+ cation forms a square pyramidal structure with five O2− anions, and a single Te6+ cation forms a six-coordinated octahedral structure with O2− anions. Since the lone-pair electron (Lp) of the square pyramidal structure, [BiO5]7−, where the Bi+ cation occupies the center of the square base plane, exists in the opposite direction of the square plane, the asymmetric environments of all four Bi3+ cations were analyzed and explored by determining the local dipole moments. In addition, to determine the extent of bond strain and distortion in the unit cell, which is attributed to the asymmetric environments of the Bi3+ and Te6+ cations in Bi6Te2O15, bond strain index (BSI) and global instability index (GII) were also calculated. We also investigated the structural, electronic, and optical properties of the structure of Bi6Te2O15 using the full potential linear augmented plane wave (FP-LAPW) method and the density functional theory (DFT) with WIEN2k code. In order to study the ground state properties of Bi6Te2O15, the theoretical total energies were calculated as a function of reduced volumes and then fitted with the Birch–Murnaghan equation of state (EOS). The band gap energy within the modified Becke–Johnson potential with Tran–Blaha parameterization (TB-mBJ) revealed a value of 3.36 eV, which was higher than the experimental value of 3.29 eV. To explore the optical properties of Bi6Te2O15, the real and imaginary parts of the dielectric function, refraction index, optical absorption coefficient, reflectivity, the real part of the optical conductivity extinction function, and the energy loss function were also calculated.

A comparative study of physical and thermoelectrical characteristics of the new full‐Heusler alloys Ag2TiGa and Ag2VGa with ab initio calculations

AbstractThis paper will focus on the comparative study of the structural, electronic, magnetic, optical, and thermoelectric properties of the two Heusler systems Ag2TiGa and Ag2VGa in the inverse L21 Hg2CuTi structure. Using the density functional theory‐based wien2k code, which implements the computational methods used in this study, namely GGA, GGA‐mBJ, GGA + U, and GGA + SOC (spin‐orbit coupling). The band structures show that all two structures studied are metallic. The spin density of states of Ag2VGa has evident spin splitting near the Fermi level, and the total magnetic moment of the Ag2VGa structure is 2.19 μB, which indicates that Ag2VGa is magnetic. The full‐Heusler Ag2VGa material can be used as spintronic materials due to their high spin polarization (about 50%). While Ag2TiGa has low polarization so it is bad electronically, but better thermoelectrically than Ag2VGa. So, the full‐Heusler Ag2TiGa material may also be considered as a potential candidate for thermoelectric applications at room temperature. Studies of the two new Heusler alloys may provide a theoretical reference for subsequent theoretical research and experimental synthesis of Ag‐based Heusler alloys.