Johnson Exchange Potential Research Articles

First‐Principles Study of Structural and Elastic, Electronic, and Thermoelectric Properties of PdSe2

The thermoelectric material in orthorhombic (Pbca) phase is studied with the help of density functional theory implemented in WIEN2k. The main properties of investigated are elastic, electronic, and thermoelectric properties. The anisotropy factors obtained with the elastic constants indicate that is strongly anisotropic. The Tran and Blaha‐modified Becke–Johnson exchange potential is used for bandgap calculations. The BoltzTraP code is used to find out the thermoelectric properties of . At 300 K, the maximum value of the Seebeck coefficient is 200 μV K−1 for the hole carrier concentration of 2.5 × 1019 cm−3 and is 241 μV K−1 for the electron carrier concentration of 1.2 × 1019 cm−3. The power factor (PF) and figure of merit (ZT) are calculated for different carrier concentrations and temperatures. The optimum value of ZT for bulk PdSe2 as calculated in this work is ≈0.6 for hole carrier concentration (p = 2.6 × 1020 cm−3) at 800 K, which suggests as a potential material in thermoelectric applications at higher temperatures.

Unveiling half-metallic, thermoelectric and optoelectronic behavior of the new Heusler alloy RbCrZ (Z = Si, Ge): a DFT perspective

Abstract Utilizing the density functional theory (DFT) method, this study aims to predict with precision the structural, elastic, electronic, magnetic, thermoelectric, thermal, and optical properties of two recently discovered half-Heusler alloys, namely RbCrSi and RbCrGe. The exchange and correlation potential are accounted for using the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE) and the Tran–Blaha-modified Becke–Johnson exchange potential (TB-mBJ). Through structural analysis, it is observed that both RbCrSi and RbCrGe alloys exhibit energetic stability in a type-3 structure with a ferromagnetic (FM) state. Both alloys exhibit half-metallic properties and integer magnetic moments of 3 μB, following the Slater-Pauli rule. Additionally, elastic calculations confirm their mechanical stability and anisotropic ductile behavior. The quasi-harmonic Debye model (QHDM) is employed for calculating thermodynamic properties, while the BoltzTraP code, based on semi-classical Boltzmann theory (SCBT), is utilized for evaluating thermoelectric properties. Findings reveal that RbCrZ alloys (with Z = Si, Ge) exhibit high figure of merit (ZT) values nearing unity at highest temperature. Consequently, the newfound half-Heusler alloys RbCrSi and RbCrGe hold significant promise for applications in thermoelectricity and spintronic devices. This comprehensive analysis underscores the potential of these alloys in the realm of renewable energy applications.

New insights into the bonding, electronic and optical properties of fergusonite and scheelite ReNbO4 (Re = Y, La and Lu) compounds

A systematic study of the structural, bonding, electronic, and optical properties of the ReNbO4 (Re = Y, La, and Lu) compounds with the fergusonite (space group I/2a) and scheelite (space group I41/a) structure was performed using density functional theory calculations. The aim of these calculations was to resolve some doubt about these properties for the fergusonite phase and to fill the existing knowledge gap for the scheelite phase. To carry out geometry optimization, the generalized gradient approximation for solids was used. Based on these optimized crystal structures, the bonding, electronic and optical properties were determined using the modified Becke and Johnson exchange potential. An analysis of the bonds between Nb and O atoms showed that Nb atoms in the fergusonite structure of the rare-earth niobates were octahedrally coordinated to oxygen atoms, unlike in the scheelite phase, which had tetrahedral coordination. The calculated values of the direct energy band gap for the fergusonite YNbO4, LaNbO4 and LuNbO4 compounds were 4.435, 4.427 and 4.431 eV, respectively. The optical spectrum for these systems is characterized by a small exciton binding energy, which affects the experimental prediction of the energy band gap when the Tauc plot method is used. The values for the energy band gap in the scheelite phase were 4.625 eV for YNbO4, 4.844 eV for LaNbO4 and 4.611 eV for LuNbO4 and all were indirect. The real and imaginary parts of the dielectric tensor were computed up to 25 eV for both phases, and were interpreted based on their electronic structure. The lower energy regions of the optical spectra of these systems are mainly due to electronic transitions within the NbO6 polyhedron (for the fergusonite phase) and the NbO4 polyhedron (for the scheelite phase), i.e., electronic transitions from the occupied O-2p states at the top of the valence band to the unoccupied Nb-4d states at the bottom of the conduction band.

First-principles investigation of structural electronic magnetic and thermodynamic properties of CdS alloyed with Co transition metal

This research work investigates the structural, electronic, and magnetic properties of Cd1–xCoxS compounds. The supercells with 16 atoms have been studied by substituting a Cd atom with a Co atom in the cubic unit cell CdS from x = 0 to x = 1 in a Zinc-Blende structure based on the first principles of spin-polarized density functional theory as implemented in the WIEN2k code. The full potential augmented plane wave method FP-LAPW (Full potential linear augmented plane wave) was used in this study to evaluate the structural properties of the compounds, the exchange–correlation term is based on the PBE-GGA (Perdew–Burke–Ernzerhof generalized gradient approximation). For other properties, such as electronic structures, densities of states, and magnetic properties, the TB-mbj GGA (Tight Binding modified Becke–Johnson) exchange potential approximation is utilized. In addition to these properties, the thermodynamic properties were added advantage to clarify their comportment as temperature variation. The analysis of the density of spin-polarized states showed the ferromagnetic character with a from x = 0.125 to x = 0.875. The calculated total magnetic moments of Cd1–xCoxS are addressed concerning the change in lattice parameters. To track the shift brought on by adding Co, we ran our calculationsfrom x = 0.125 to x = 0.875 for Cd1–xCoxS compounds. Hence, the negative energyformation indicates that our compound can be made experimentally. The material may be used for solar cell applications. In summary, our findings represent a guide for future research. The findings of this work might provide useful direction for the usage of this alloy system in a variety of device applications, For example in high-efficiency tandem solar cells, magnetic sensors, and photoconductive detector applications.

First Principle Study of Structural, Electronic, Optical Properties of Co-Doped ZnO

In this theoretical study, the electronic, structural, and optical properties of copper-doped zinc oxide (CZO) were investigated using the full-potential linearized enhanced plane wave method (FP-LAPW) based on the density functional theory (DFT). The Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ) was employed to enhance the accuracy of the electronic structure description. The introduction of copper atoms as donors in the ZnO resulted in a reduction in the material’s band gap from 2.82 eV to 2.72 eV, indicating enhanced conductivity. This reduction was attributed to the Co-3d intra-band transitions, primarily in the spin-down configuration, leading to increased optical absorption in the visible range. The Fermi level of the pure ZnO shifted towards the conduction band, indicating metal-like characteristics in the CZO. Additionally, the CZO nanowires displayed a significant blue shift in their optical properties, suggesting a change in the energy band structure. These findings not only contribute to a deeper understanding of the CZO’s fundamental properties but also open avenues for its potential applications in optoelectronic and photonic devices, where tailored electronic and optical characteristics are crucial. This study underscores the significance of computational techniques in predicting and understanding the behavior of doped semiconductors, offering valuable insights for the design and development of novel materials for advanced electronic applications.

Tailoring the photocatalytic properties of anatase TiO2 by B–TM (TM = Pt, Ta, V) co-doping

In order to provide insight into the influence of co-doping with boron (B) and transition metals (TM = Pt, Ta, V) on the photoactivity of anatase TiO2, the electronic, structural and optical characteristics of the mentioned co-doped systems were studied using density functional theory calculations and the modified Becke–Johnson exchange potential. For each transition metal two cases were considered, with B atom either replacing O atom (B-substitutional) or imbedding interstitially (B-interstitial) into TiO2 lattice. The calculations showed that the co-doping is more favorable for the B-interstitial systems than for the B-substitutional ones and under the O-rich conditions. For the B-substitutional cases a slight decrease of the band gap is observed. In contrast, the results obtained for the B-interstitial systems exhibited no band gap narrowing. However, in these systems, the occurrence of localized states within the band gap is noticed, which could improve visible light absorption through a two-step optical transition.

Electronic, optical, phonon, polaron, carrier transport and scintillation properties of Cesium Hafnium Halides Cs2HfX6, (X = CI, Br and I)

In this work, we investigated the electronic, optical, phonon, polaron, and transport properties of cesium hafnium halides Cs2HfX6, X=Cl, Br and I and estimated their upper light yield. Using First-principles calculations combined the exchange-correlation energy of the Generalized Gradient Approximation GGA with the modified Becke–Johnson exchange potential (mBJ) and the spin-orbit coupling (SOC), these materials demonstrated discrete valence and conduction bands with low band dispersion and direct band gap decreasing as Cs2HfCl6 (5.48 eV)→ Cs2HfBr6(4.18eV)→ Cs2HfI6 (2.72 eV). These obtained values are very close to the available experimental ones. Likewise, the band edge curvature of both valence band maximum (VBM) and conduction band minimum (CBM) reflects the heavier effective mass of electron at CBM Cs2HfCl6(7.58m0),Cs2HfBr6(5.94m0),Cs2HfI6(3.92m0) compared to that of the hole at VBM Cs2HfCl6(6.12m0),Cs2HfBr6(3.72m0),Cs2HfI6(2.34m0). Moreover, these materials exhibited a high transmittance rate, in their emission range, about: 93.57 % for Cs2HfCl6 91.25 % for Cs2HfBr6 and 88.1 % for Cs2HfI6, which is adequate to minimize the scintillated photons loss. The phonon dispersion and the normal modes for Γ point were calculated and discussed. Only three longitudinal optical phonon modes were identified active and their contribution to the ionic dielectric constant was calculated. Having First-principles results, polaron properties, the temperature dependence of polaron mobility, and relaxation time were calculated. These materials showed moderate electron (hole)-phonon couplings αe=6.72(αh=6.04) for Cs2HfCl6,αe=8.26(αh=6.54) for Cs2HfBr6 and αe=6.16(αh=4.76) for Cs2HfI6 compared to other polar materials leading to large polaron mass, high scattering rate, small relaxation time, and low electron (hole) room-temperature mobility 0.14cm2V−1s−1 (0.23 cm2V−1s−1) for Cs2HfCl6 0.14cm2V−1s−1 (0.45 cm2V−1s−1) for Cs2HfBr6 and 0.62cm2V−1s−1 (1.81 cm2V−1s−1) for Cs2HfI6which has only a positive role via the increase of the recombination yield. While such low mobility definitely limited their use in solar cell applications. Moreover, the upper light yield of these materials was estimated for the polaron and simple phenomenological models by taking the needed material inputs to these models from First-principles calculations. The results of latter one were 58,290 photon/MeV for Cs2HfCl6 76,685photon/MeV for Cs2HfBr6 and 118,000photon/MeV for Cs2HfI6 compared to the maximum experimental values 54,000 photon/MeV for Cs2HfCl6 61,500photon/MeV for Cs2HfBr6 and 70,000photon/MeV for Cs2HfI6. These computational findings may add strong evidence for suggesting experimental improvement of the crystal growth conditions and explain the remarkable scintillation properties of these materials as new and efficient gamma- and X-rays scintillators.

Ab-initio investigations for structural, optoelectronic and thermoelectric properties of Li2BeXSe4 (X = Ge, Si, Sn) compounds

Motivated by photovoltaic activities, we study certain aspects of the stannite structure (ST) of the Li2BeXSe4 (X = Ge, Si, Sn) compounds using the full potential augmented plane wave approach implemented in the Wien2k code. Concretely, we use the generalized gradient approximation (GGA) and the modified Becke–Johnson exchange potential (mBJ) to evaluate in a precise way, the band gaps, the total and the partial densities, as well as the optical and the thermoelectric properties. Among others, we show that the Li2BeXSe4 (X = Ge, Si, Sn) semiconductors exhibit a direct band gap in the Γ point of the Brillouin Zone (BZ). Furthermore, the optical properties of the three compounds show a strong optical conductivity and a good optical absorption. As a result, we reveal that the proposed materials are suitable for the application in photovoltaic solar cells. Using the BoltzTrap package, we also examine and discuss the thermoelectric properties such as the Seebeck coefficient (S), the electrical conductivity, and the thermal conductivity as a function of the temperature. We find that the Li2BeXSe4 (X = Ge, Si, Sn) compounds exhibit good thermoelectric transport properties, making them a good candidates for clean energy applications.

Energy Bandgap of Cd1−xZnxTe, Cd1−xZnxSe and Cd1−xZnxS Semiconductors: A First-Principles Analysis Based on Tran–Blaha–Modified Becke–Johnson Exchange Potential

Energy Bandgap of Cd1−xZnxTe, Cd1−xZnxSe and Cd1−xZnxS Semiconductors: A First-Principles Analysis Based on Tran–Blaha–Modified Becke–Johnson Exchange Potential

DFT investigations of optoelectronic and thermoelectric properties of stannite phase of Cu2SrXSe4 (X = Ge, Si, Sn) compounds using TB-mBJ mechanism

Using the density functional theory (DFT) computations implemented in WIEN2K package and Boltzmann theory with the BoltzTrap code, we study certain physical properties of a new class of Cu2SrXSe4 (X = Ge, Si, Sn) materials. Concretely, we investigate the electronic, the optical and the thermoelectric aspects of such materials from the generalized gradient approximation (GGA) corrected by the Tran Balaha modified Becke–Johnson exchange potential (GGA+TB-mBJ). Analyzing the computed electronic properties, we show the semiconducting nature of these compounds. Precisely, we reveal that these compounds involve an indirect band gap with p type. This electronic aspect is very important for the absorber solar cell layers due to the fact that the length diffusion of the electron is larger than the one of the hole. We find that the obtained gap values of such a new family inspired by CZTS materials can be compared with various absorber layers. For the Cu2SrSnSe4 model, we observe similar behaviors compared to the silicon solar cell absorber layers. Using the scalar dielectric function, we investigate the optical properties of the studied materials. Precisely, we obtain that such a family of materials involve higher values of the absorption coefficient in the visible and the ultra violet light spectrum. For each material, we observe that the absorption starts at the corresponding band gap energies. Exploiting Boltzmann theory with the BoltzTrap code, we compute and examine the thermoelectric properties such as the Seebeck coefficient, the thermal conductivity, the electrical conductivity, and the figure of merit as a function of the temperature. As a result, we show that the studied materials involve a high absorption spectra and a good figure of merit (ZT) showing relevant features for photovoltaic and thermoelectric applications.

Investigation of X2GaAgCl6 (X = K, Cs) for Optoelectronic Devices: A Density Functional Theory Study

The electronic, elastic, structural, and optical properties of X2GaAgCl6 (X = K, Cs) are investigated by using the full potential linearized augmented plane wave (FP‐LAPW) method based on density functional theory (DFT). Generalized‐gradient approximation (GGA) is used along modified Becke–Johnson (mBJ) exchange potential. K2GaAgCl6 and Cs2GaAgCl6 reveal the direct bandgap (E g) of 2.57 and 2.63 eV, respectively, at Γ symmetry points. The negative values of formation enthalpy (−1.694 for K2GaAgCl6 and −1.798 for Cs2GaAgCl6) and value of tolerance factor (τ) close to unity (0.82 for K2GaAgCl6 and 0.89 for Cs2GaAgCl6) confirm the stable nature of X2GaAgCl6 (X = Cs, K) compounds in cubic phase. Optical properties such as absorption coefficient α(ω), optical conductivity σ(ω), reflectivity R(ω), extinction coefficient k(ω), refractive index n(ω), and dielectric constants (ε 1 and ε 2) are calculated. The ε 2(ω) spectrum of Cs2GaAgCl6 and K2GaAgCl6 shows highest absorption peaks at 4.8 and 4.9 eV, respectively. The highest absorption is observed from Cs2GaAgCl6 at 7.44 eV and from K2GaAgCl6 at 7.46 eV energies. It is also noted that A2GaAgCl6 (A = K, Cs) compounds are elastically stable, anisotropic, and ductile. Investigation of elastic, structural, and optical properties shows that the compounds M2GaAgCl6 (M = Cs, K) can be potential candidates for optoelectronic applications.

Performance of the modified Becke–Johnson potential employing the pseudopotential plane-wave approach for band structure calculations

The modified Becke–Johnson exchange potential combined with local-density approximation correlation (mBJLDA) has recently attracted interest because it provides highly improved band gaps at a very low computational cost. In this work we performed an extensive investigation of the performance of the mBJLDA potential employing a norm-conserving pseudopotential plane-waves approach (mBJLDA@PP), as implemented in the abinit code, using a test set of 83 solids representing a wide range of semiconductors and insulators. Our results confirm the conclusion of our previous study that the number of electrons treated as valence in the pseudopotentials of the cations can have a significant impact on the calculated mBJLDA@PP band gaps. More specifically, while the use of typical pseudopotentials leads to accurate band gaps of certain systems, it yields significantly underestimated band gaps for other systems compared to experiment and to those of the all-electron mBJLDA (mBJLDA@AE) approach. The classes of the latter systems are identified, and this problem is resolved by including some outer core states as valence. The resulting mean absolute error in the calculated band gaps (compared to experiment) is of 0.46 eV, which is comparable to that of the mBJLDA@AE band gaps, reflecting the accuracy and reliability of the mBJLDA@PP approach for the band gap calculations.

Optical and thermal properties of the half-Heusler VFeSb and NbFeSb alloys

In this work, we used the First-principles method Fplapw based on density functional theory (DFT) to study the thermal and optical properties of Half-Heusler compounds VFeSb and NbFeSb. These materials are characterized with a small and narrow band gap semiconductors close to the fermi level; following the electron number and other structural properties of these materials have a high performance thermoelectric .In our calculations, we will use the structural and electronic properties for our materials already calculated in previous publications. The modified Becke–Johnson exchange potential (mBJ)-LDA approach was also used. Optical properties such as complex dielectric function, refractive index, reflectivity, energy loss function for incident photon energy up to 30eV have been predicted. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the Half-Heusler compounds.

Electronic and optical properties of CsGeX[formula omitted]M (X ,M = Br, Cl, I) perovskites for solar cell applications: First-principles study using PBE and TB-mBJ potentials

The effect of mixed halogen composition on the structural, electronic, and optical properties of CsGeX2M (X, M=Cl, Br, I) has been studied using density functional theory, generalized gradient approximation, and modified Becke–Johnson exchange potential (TB-mBJ). The electronic properties show that all structures are direct semiconductors with wide band gaps between 1.251 eV and 1.655 eV. In addition, the band gap values of these materials are tuned by decreasing the number of chlorine or bromine atoms. PDOS analysis of CsGeX2M compounds shows that the Cs atom has negligible effects on the electronic bands of these perovskites. The major contribution to the electronic bands of these compounds close to Ef comes from the Ge orbitals and I, Br, and Cl . Optical properties show that these materials have good absorption capacity. The photon absorption coefficient along the z-axis in the visible light region is between 40 × 104 cm−1 and 65 × 104 cm−1, thanks to their narrow band gap. Furthermore, the real ɛ1 and imaginary ɛ2 parts of their dielectric functions show that CsGeBr2I, CsGeBr2Cl, CsGeCl2I, and CsGeCl2Br also possess a high ability to retain the energy they absorb.

Study of new lead-free double perovskites halides Tl2TiX6 (X = Cl, Br, I) for solar cells and renewable energy devices

In recent years, lead-free double perovskites have been found tremendously advantageous due to their unique optoelectronic and environmentally benign photovoltaic characteristics. Herein, we have explored optical, thermoelectric, and thermodynamical properties of Tl2TiX6 (where X ​= ​Cl, Br, I) using modified Becke and Johnson exchange potential. The calculated value of the Goldschmidt tolerance factor in the range 0.90–1.04 demonstrates the structurally stable cubic phase of our materials. Moreover, the negative value of formation energy together with positive phonon dispersion further reinforces the thermodynamically stable nature of the crystal structures. Further, a decrease in calculated bandgaps of Tl2TiCl6 (2.99 ​eV) was observed in Tl2TiBr6 (2.26 ​eV) and Tl2TiI6 (1.42 ​eV), obtained by changing Cl with Br and I anions, respectively. The first absorption bands 413 ​nm–310 ​nm for Tl2TiCl6, 496 ​nm–400 ​nm for Tl2TiBr6, and 775 ​nm–496 ​nm for Tl2TiI6 increase the potential of studied compounds for solar cells, and optoelectronic applications. In the end, the transport properties were examined based on Boltzmann transport theory via BoltzTrap code. Moreover, the reasonably high values of figure of merits (0.76 and 0.75) measured at room temperature further authenticate their utilization as thermoelectric generators.

Insight into the exemplary structural, elastic, electronic and optical nature of GaBeCl3 and InBeCl3: a DFT study.

In the scheme of density functional theory (DFT), Structural, elastic, electronic, and optical properties calculations of GaBeCl3 and InBeCl3 are carried out using Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ) installed in Wein2k software. Structurally the compounds of interest are found to be stable. Both compounds possess elastic stability, anisotropy, and ductility determined by the elastic studies. The electronic-band structure analysis shows the semiconductor nature of GaBeCl3 and InBeCl3 compounds with indirect band gaps of ∼3.08 eV for GaBeCl3 and ∼2.04 eV for InBeCl3 along with the symmetrical points from (X–Γ). The calculated total density of states (TDOS) and partial density of states (PDOS) of these compounds reveal that for the GaBeCl3 compound, the contribution of Ga (4p) and Cl (3p) orbital states in the valence, as well as the conduction band, is dominant. While for InBeCl3, the contribution of Cl (3p) states as well as In (5s) is large in the valence band and in that of Cl (3p-states) states in the conduction band. The type of chemical bonding is found to be ionic in both compounds. The optical properties i.e., the real (ε1(ω)) and imaginary (ε2(ω)) parts of dielectric function, refractive index n(ω), optical reflectivity R(ω), optical conductivity σ(ω), absorption coefficient α(ω), energy loss L(ω) and electron extinction coefficient k(ω) are also discussed in terms of optical spectra. It is reported that n(ω) and k(ω) exhibit the same characteristics as ε1(ω) and ε2(ω) respectively. Efficient application of these materials can be seen in semiconducting industries and many modern electronic devices.

Theoretical and experimental study of effects of Co2+ doping on structural and electronic properties of ZnO

In this study, we theoretically investigated the electronic structure of Zn1-xCoxO using different approaches for the exchange-correlation potential comprising GGA with the on-site Coulomb correlation interaction U to the Zn d orbital (GGA + UZn), GGA with modified Becke–Johnson exchange potential (GGA + mBJ), and (GGA + mBJ + UZn). To support the theoretical results, a Co2+-doped ZnO sample was obtained experimentally by using the microwave–hydrothermal method. Changes in the structural, vibrational, electronic, and magnetic properties induced by the insertion of the Co2+ impurities in the ZnO lattice were determined based on first principles calculations. The theoretical results showed that the 3d orbitals derived from Co2+ appear in the deep region of the band gap. These orbitals are responsible for the magnetic behavior of cobalt doped materials. The energy levels introduced by the Co2+ dopant ions reduced the theoretical band gap value, which was also observed experimentally. The addition of Co2+ ions weakened the Raman mode E2H intensity, which was attributed to the increasing distortion induced by doping. Photoluminescence spectroscopy results indicated a reduction in the visible emission region after adding Co2+ ions, thereby indicating the formation of alternative pathways for the recombination process.

Structural, Electronic, Magnetic, and Hyperfine Properties of V-doped SnO2 (Sn1–xVxO2, x: 0, 0.042, 0.084, and 0.125). A DFT-Based Study

Ab initio electronic structure calculations were performed to study the effect of V-doping on the structural, electronic, and magnetic properties of tin dioxide (Sn1–xVxO2, x: 0.042–0.125). Calculations have been performed using pseudopotentials and plane-wave and full potential linearized augmented plane-wave methods. State-of-the-art Heyd–Scuseria–Ernzerhof (HSE06) exchange–correlation hybrid functional and the Tran–Blaha-modified Becke–Johnson (TB-mBJ) exchange potential were employed. Our calculations showed that V4+ substitutionally replaces Sn4+ ions inducing a reduction of the volume cell of SnO2 and shortening of the metal–oxygen nearest neighbor bond lengths. Spin polarization at the V sites is predicted. Our results indicate that the magnetic ground state of the resulting system is paramagnetic. TB-mBJ and HSE06 accurately describe the experimentally reported dependence of the band gap with x. Our theoretical results for the hyperfine parameters at the Sn sites are in excellent agreement with Mössbauer experiments. Hyperfine parameters at the V sites are also presented.

The effect of zinc concentration upon electronic structure, optical and dielectric properties of Cd1− xZnxTe alloy: TB-mBJ investigation

In this paper, the structural, electronic, optical, and dielectric properties of Cd1-xZnxTe alloy are reported using (FP-LAPW) method based on DFT, within GGA, LDA approximations, and Tran–Blaha-modified Becke–Johnson (TB-mBJ) exchange potential. Energy gaps, dielectric function, refractive index, static dielectric constant, and the reflection coefficient have been determined and their variation as a function of zinc concentration has been analyzed and discussed. All studied parameters are found to vary nonlinearly with Zn concentration ongoing from CdTe (x = 0) to ZnTe (x = 1). The direct Γ- Γ, W–W, L-L and indirect Γ- W and Γ- L bands gaps are determined. The results will be of practical use to the community of crystal growers, semiconductor challenges, and new alloys designers.

Theoretical investigations of structural, mechanical, electronic and optical properties of NaScSi alloy

Ab initio density functional theory is employed to investigate the structural, elastic, electronic and optical properties of the half-Heusler NaScSi alloy. The lattice constants are very near to the available theoretical data. In addition, besides the GGA approximation, the modified Becke–Johnson exchange potential is also used to improve the direct X→X band gap value. Furthermore, the elastic constants and related elastic moduli confirm its stability and brittle behaviour in the type I structure. The influence of pressure on Cij constants, bulk modulus B, Cauchy pressure, Poisson ratio ν, shear modulus, B/G ratio and anisotropy factor A are analysed. Additionally, the strong absorption is extended between the visible domain and that of the ultraviolet is predicted.