Tran-Blaha Modified Becke-Johnson Exchange Research Articles

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.

Unveiling the potential of CuAlxGa1−xSe2 (x = 0.25) chalcopyrite as absorbent for photovoltaic application: first-principles insights into the structural, elastic, mechanical, electronic, thermodynamic and optical properties

This study explores the structural, elastic, mechanical, electronic, and optical properties of CuAlxGa1−xSe2 (x = 0.25) chalcopyrite, a crucial material in photovoltaic cells. Utilizing type II-IV-V2 chalcopyrite, widely employed in high-efficiency solar cell production, we employ first-principles calculations with Tran–Blaha-modified Becke–Johnson exchange potential techniques. We aim to determine the band gap and optical properties to understand the compound’s morphology, crucial for solar cell development. Results show CuAlxGa1−xSe2 as a 1.36 eV direct band gap semiconductor. Optical characteristics, including dielectric tensor components and absorption coefficient, are calculated to assess its suitability for solar cell applications. Predictions of Young’s modulus E, Poisson’s ratio ν, bulk B, and shear G moduli provide insight into the crystal’s mechanical behavior. Additionally, phonon, dynamical stability, and thermodynamic properties are discussed, shedding light on the material’s potential in photovoltaic technology.

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.

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

Effect of hydrostatic strain on the mechanical properties and topological phase transition of bi-alkali pnictogen NaLi2Bi

The bi-alkali pnictogens have attracted significant attention for optoelectronic and photocathodic device applications. However, in most of the compounds belonging to this family, there has been less effort put into investigating the mechanical properties and topological phase transitions (TPT) of the compounds. Here, in the framework of density functional theory, the mechanical properties and topological phase transition of NaLi2Bi under hydrostatic pressures are investigated. Elastic constants and phonon calculations have shown the mechanical and dynamical stability of this compound under hydrostatic tension and compression. The analysis of the elastic constants show that the NaLi2Bi in the equilibrium state is an auxetic material with a negative Poisson’s ratio of -0.285, which changes to a material with a positive Poisson’s ratio under hydrostatic tension. Meanwhile, Poisson’s ratio and Pugh ratio indicate that this compound has brittle behavior and maintains it under hydrostatic pressures. The calculated results of the band structure within the generalized gradient approximation (GGA) (Tran-Blaha modified Becke-Johnson exchange potential approximation (TB-mBJ)) show that NaLi2Bi is a nontrivial topological material (trivial topological material). It was found that hydrostatic compression (tension) in the GGA (TB-mBJ) approach leads to a transition from a nontrivial (trivial) to a trivial (nontrivial) topological phase for this compound. Moreover, the calculated Wannier charge centers confirm the TPT. Identifying the mechanisms controlling the auxetic behavior and TPT of this compound offers a valuable feature for designing and developing high-performance nanoscale electromechanical and spintronic devices.

DFT Investigation of the Structual and Optoelectronic Properties of Alkali Metal Hydrides MH (M=Li, Na)

This paper presents ab initio calculations within the Density Functional Theory (DFT) for the structural and optoelectronic properties of the alkali metal hydrides LiH and NaH in rocksalt structure (B1). This study used the Generalized Gradient Approximation (GGA) of Wu-Cohen to consider the electronic exchange and correlation interactions. In addition, the Tran-Blaha modified Becke-Johnson exchange potential was used with the GGA approach (GGA-TBmBJ) to calculate the band structure with high accuracy. The structural properties, namely the lattice parameter, the bulk modulus, and the pressure derivative of the bulk modulus were determined and found to be generally in good agreement with other research findings. Furthermore, the energy band gaps, the Density Of States (DOS), the static and high-frequency dielectric constant, along the refractive index were addressed and analyzed. These results could be useful for hydrogen storage purposes.

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.

Toward accurate electronic, optical, and vibrational properties of hexagonal Si, Ge, and Si1−xGex alloys from first-principle simulations

A new hexagonal phase of Si1−xGex alloys have been successfully synthesized through efforts in recent reports. Utilizing the combined first-principle calculations and special quasi-random model, we precisely investigated the structural, electronic, optical, and vibrational properties of hexagonal Si and Ge and disordered hexagonal Si1−xGex random alloys. We found a large negative deviation between the calculated lattice constants within the revised Perdew–Burke–Ernzerhof for solids functional and the linear fitting results. The electronic structures obtained by using the Tran–Blaha modified Becke–Johnson exchange potential confirm that hexagonal Si1−xGex (x > 0.625) alloys present direct bandgaps. Through solving the Bethe–Salpeter equation, the linear optical spectra of hexagonal Si and Ge are demonstrated. We reveal that the peaks of complex dielectric functions are redshifted with the addition of Ge atoms. Also, the real and imaginary parts exhibit strong anisotropy, which makes hexagonal Si1−xGex alloys potentially useful as nonlinear crystals. The transition is allowed in the infrared region for the hexagonal Si1−xGex (x > 0.625) alloys, and the linear optical spectra can be continuously tuned over a wide range of frequency with Ge addition in the infrared region. Furthermore, density-functional perturbation theory calculations were carried out to predict the off-resonance Raman activity. The results suggest that the vibrational modes of the Si–Si bond exhibit a strong dependency on the compositions, which provides a useful way to identify the most probable atomic configurations of hexagonal Si1–xGex alloys in future experiments.

Investigation of the photovoltaic properties of BaHf1-xZrxS3 ([formula omitted]) chalcogenide perovskites using first principles calculations

Electronic, optical, and photovoltaic properties of BaHf1-xZrxS3 (x = 0.00, 0.25, 0.50, 0.75, and 1.00) alloys were evaluated using first principles calculations via the density functional theory. The exchange-correlation potential is treated with generalized gradient approximation. Additionally, the Tran–Blaha modified Becke–Johnson exchange potential is employed, because it gives very accurate results of the band gap in solids. The band structure calculations reveal that these compounds exhibit a semiconductor behavior with a small band gap (Eg < 2 eV). To investigate the optical transitions in these compounds, the real and imaginary parts of the dielectric function are examined. The coefficient absorption (α) is calculated and discussed as well. We found a remarkable α exceeding 105 cm−1 near Eg, which is suitable for the absorption of visible light. To exploit the high photo-absorptivity and evaluate the photovoltaic performance of these alloys, the power conversion efficiency is computed using the spectroscopic limited maximum efficiency method. Our predicted alloys have the characteristics required for photovoltaic applications with a maximum photovoltaic efficiency (η) between 22.22% and 30.09% for thickness L = 500 nm. Particularly, BaHf0.75Zr0·25S3 reveals a performance comparable to that of the best-known photovoltaic materials such as CH3NH3PbI3.

Structural, electronic and optical modeling of perovskite solar materials ASnX3 (A = Rb, K; X = Cl, Br): First principle investigations

In this paper, we present structural, electronic and optical response for inorganic lead-free tin halide perovskites ASnX3 (A = Rb, K; X = Cl, Br) compounds, to examine their possible utilization as future photovoltaic materials. The structural optimization, energy band structure, density of states and exhaustive optical spectra for these perovskite compounds are delved using the Tran-Blaha modified Becke-Johnson exchange and correlation potential as implemented in Wien2k code. Optical performance of the compounds is accomplished through the investigation of real & imaginary dielectric tensor components, optical absorption, reflectivity and refractivity spectra. Direct band gap for RbSnCl3 (RbSnBr3) and KSnCl3 (KSnBr3) compounds is obtained as 1.46 (0.98) eV and 1.48 (0.93) eV, respectively which lies within standard photo-voltaic range. Results obtained in present computations are in decent agreement with earlier reported data, which firmly endorse the accuracy of present calculations. In addition, band gap reduction is perceived while switching from X = ‘Cl’ to ‘Br’ which has also revealed the enhancement in integrated absorption coefficient. Promising electronic and optical properties obtained for these perovskite compounds affirms their potential utilization in photo-voltaic and other opto-electronic applications.

Study of optoelectronic and transport properties of MgLu2Z4 (Z=S, Se) spinels for optoelectronic and energy harvesting applications

Intense research has been done to build materials that are potential candidates for energy storage applications. Spinels are of great interest in this respect because they have vast potential to be used in Mg-based batteries. To explore their energy storage as well as transport response, we calculate Mg-based spinels, namely MgLu2Z4 (ZS, Se). The full potential linearized augmented plane wave method has been used to examine their optoelectronic and transport response. An increase in the lattice constant has been observed by replacing S with Se, and our calculated values are in good agreement with those obtained experimentally. The Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJ), has been used to study the optoelectronic and thermoelectric characteristics of the respective spinels. The dependence of these properties on the bandgap has also been observed. Replacing S with Se resulted in the transformation of the electronic bandgap from near-infrared to the visible region (MgLu2S4: 2.60 eV and MgLu2Se4: 2.00 eV). These results showed that these materials have the potential to be used in optoelectronic devices. The optical properties are discussed as a function of energy. Besides, the thermal transports are discussed with the help of Seebeck coefficient and figure of merit as a function of chemical potential and temperature.

New equiatomic quaternary Heusler compounds without transition metals KCaBX (X = S and Se): Robust half-metallicity and optical properties

It is known that high spin-polarization and magnetism can be found even in materials with neither transition metals nor rare earths. In this paper, we report results of the structural design, electronic structure, magnetic and optical properties of new equiatomic quaternary Heusler (EQH) KCaBX (X = S and Se) compounds. Electron exchangecorrelation interactions are described by the Wu-Cohen (WC) functional and Tran-Blaha modified Becke-Johnson exchange (mBJ) potential. Ferromagnetic ordering is stable for the cubic structure of space group F43 m in which the K, Ca, B and X atoms are located at 4c, 4d, 4a and 4b Wyckoff positions, respectively. Quaternaries at hand exhibit a perfect spin-polarization around the Fermi level, which is a result of the half-metallicity with metallic spin-up channel and semiconductor spin-dn channel. The ferromagnetic half-metallic and spin-flip band gaps are 2.648(2.470) and 0.673(0.526), respectively, for KCaBS(KCaBSe). Both studied compounds have a total magnetic moment of 2.000 μB. Additionally, the strain effect on the electronic and magnetic properties is also examined. Finally, the optical properties of the KCaBX alloys are investigated for energies up to 25 eV. Optical spectra show the metallic behavior at extremely low energies and semiconductor nature at higher energies. Interestingly, KCaBS and KCaBSe exhibit prospective absorption properties with a quite large absorption coefficient in the ultraviolet regime.

Optoelectronic properties of three PbSe polymorphs

The narrow bandgap PbSe has attracted a remarkable interest from the researchers in recent years for their potential optoelectronics and photovoltaic applications. In this article, we report the optoelectronic properties of cubic (NaCl-type) and orthorhombic (Cmcm- and Pnma-type) polymorphs of PbSe using the density functional theory based first-principles approaches. In accordance with the available literature, the NaCl–PbSe has been found stable in the ground state, whereas the Cmcm-, Pnma-types of PbSe have been realized at intermediate pressure of ~4.5 GPa. The electronic structures and optical spectra of these polymorphs have been determined using the Tran-Blaha modified Becke-Johnson exchange potential with and without spin-orbit coupling (SOC) effects. The inclusion of SOC has shown important effects on the electronic structures and consequently on the optical spectra. Despite SOC driven energy gap narrowing of these polymorphs, the direct bandgap nature of Cmcm-PbSe calculated with TB-mBJ has changed to indirect nature with the inclusion of SOC. Moreover, our results of the optical spectra of NaCl–PbSe have shown that this phase is isotropic, whereas a sufficiently high degree of anisotropy in the optical spectra has been recorded for Cmcm-, Pnma-types of PbSe. These PbSe polymorphs exhibited a high optical absorption that approaches as large as 106 cm−1. Moreover, our study provides comprehensive details of exciton binding energies and plasmon energies. This work is believed to provide a strong foundation to exploit the optoelectronic character of the studied phases of PbSe for next-generation optoelectronic and photovoltaic applications.

DFT prediction of structural, electronic and magnetic properties of Sr0.75TM0.25S (TM is 3d transition metals)

ABSTRACTIn recent years, the scientific community has done great efforts to search for new materials suitable for spintronics applications. Diluted magnetic semiconductors have been considered as prospective candidates to be used in spintronic devices. In this paper, we have used the full-potential linearised augmented plane wave (FP-LAPW) method within density functional theory framework to study the structural, electronic and magnetic properties of the strontium sulfide SrS doped with 3d transition metals (TM) with TM concentration (). The generalised gradient approximation proposed by Wu-Cohen (GGA-WC) was adopted to deal with the exchange-correlation effect and the Tran–Blaha modified Becke–Johnson exchange potential was also employed to calculate the electronic and magnetic properties in order to obtain accurate results. Our calculations show that the SrS doped with Ti, V, Cr, Mn, Fe and Ni are half-metallic with relatively wide ferromagnetic band gap E. However only five materials, namely, , , , and may be candidates for spintronic applications as they exhibit a wide half-metallic band gap of 1.002, 0.587, 1.201, 0.533 and 0.661 eV, respectively. Finally, results indicate that TM atoms are those that determine the magnetic properties of materials at hand.

An assessment of the structural, electronic, optical and thermoelectric properties of the BaAg2GeS4 compound

A detailed theoretical investigation on the structural, electronic, optical and thermoelectric properties of the quaternary BaAg2GeS4 compound is presented in this paper. Within the framework of density functional theory (DFT), calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method are performed. The band gap obtained using the Tran-Blaha modified Becke-Johnson exchange potential shows improved values as compared with the generalized gradient approximations with the Wu-Cohen version (GGA-WC). Therefore these results are used to determine the optical and thermoelectric properties. Results show that the BaAg2GeS4 compound is an indirect gap semiconductor. It can be used as effective ultraviolet absorber provided that it exhibits a wide absorption band and high absorption coefficient up to 182.820 (104/cm). Thermoelectric properties results show promising characteristics of the studied compound, with the best doping being in the range of 1.1×1018 and 1.3×1019 (cm−3) depending on the working temperature.

First principles insight into the structural, electronic, optical and thermodynamic properties of CsPb2Br5 compound

The ternary CsPb2Br5 compound is a promising candidate for optoelectronic applications, however, its electronic properties are not well understood yet. In this work, the structural, electronic, optical and thermodynamic properties have been systematically examined using first-principles calculations. The exchange-correlation potentials are included in the calculations through the generalized gradient approximation (GGA-PBESol) and Tran-Blaha modified Becke-Johnson exchange (mBJ) potential. Obtained structural parameters match well with the experimental data. The CsPb2Br5 compound is an indirect semiconductor with a band gap of 3.589 eV predicted by mBJ potential. A wide absorption band in the ultraviolet region with very high absorption coefficient was observed for the ternary at hand. Finally, the thermodynamic behaviors of CsPb2Br5 are also computed using the Debye quasi-harmonic model. Properties are investigated as a function of pressure up to 25 GPa under different temperatures, and discussed in details.

Examining the uniform strain effect on elastic, electronic and optical properties of CsPbCl3 through FP-LAPW calculations

We study comprehensively the uniform strain effect on the elastic, electronic and optical properties of the perovskite CsPbCl3 using theoretical calculations based on the Full-Potential Linearized Augmented Plane-Wave (FP-LAPW) method. The Generalized Gradient Approximation (GGA-PBESol) and Tran-Blaha modified Becke-Johnson exchange potential improved by Koller (KmBJ) are adopted to describe the electron exchange-correlation interactions. The compound is elastically stable and ductile. And its mechanical resistance increases with the compressive strain but decreases with the tensile stress. Based on results, CsPbCl3 is a direct semiconductor with band gap of 2.990 eV, which increases when the strain switches nature from compressive to tensile. The optical absorption of CsPbCl3 can be enhanced by applying a compressive strain, and the absorption band can be widen to 620 nm in the visible region with a compressive strain of −5%, making it suitable for photovoltaic applications. Therefore, the strain engineering on CsPbCl3 may be very useful to determine suitable parameters for applications in the optoelectronics industry.

On the structural, electronic, optical and thermoelectric properties of CdIn2Se4 ordered-vacancy compound

In this paper, we report results of the structural, electronic, optical and thermoelectric properties of CdIn2Se4 compound. These properties are investigated using first-principles calculations based on the full-potential linearized plane-wave (FP-LAPW) technique within the framework of density functional theory (DFT) and semiclassical Boltzmann transport theory. During the structural optimization, the electron exchange-correlation potentials are described through Wu-Cohen (WC) functional, while the Tran-Blaha modified Becke-Johnson exchange potential is employed when calculating the electronic and related properties to obtain more accurate band gap. Electronic band structures reveal that the CdIn2Se4 compound is a direct gap Γ−Γ semiconductor, with a band gap of 1.834 ​eV. Results of the compound optical properties suggest this material as promising absorber to work under ultraviolet radiation. Finally, the thermoelectric properties such as Seebeck coefficient, electrical conductivity, electronic thermal conductivity, power factor and dimensionless figure of merit are calculated and analyzed in details. With a proper hole doping level, the CdIn2Se4 compound can a promising candidate for thermoelectric applications with figure of merit close to unity.

Computational investigation of the structural, electronic, optical and thermoelectric properties of T2-Al2MgC2 compound

In this paper, we report the results of theoretical calculation on the structural, electronic, optical and thermoelectric properties of 2T-Al2MgC2 compound. These properties are investigated through the calculations based on the density functional theory and Boltzmann transport theory. Our calculated structural parameters are in very good agreement with other experimental and theoretical values available in the literature. Studied material has an indirect band gap KΓ−L of 2.579 eV calculated with the Tran-Blaha modified Becke-Johnson exchange (mBJ) potential, which is higher than those obtained with the standard functionals. 2T-Al2MgC2 compound has a wide absorption band from the high energy zone of visible to ultraviolet region. While it shows the transparent properties when the photon energy is lower than 2.579 eV and beyond 25 eV. Considered ternary is a good thermoelectric material with high thermopower and the figure of merit close to unity. At the hole (electron)-doping level of 1×1017 (cm−3), the calculated figure of merit is 0.98 (0.97).

First principles prediction of the elastic, electronic and optical properties of Sn3X4 (X = P, As, Sb, Bi) compounds: Potential photovoltaic absorbers

We report a first-principles study of structural, mechanical and optoelectronic properties of the Sn3X4 (X = P, As, Sb, Bi) compounds. The calculations were performed using the full-potential linearized augmented plane wave approach (FP-LAPW). The structural and mechanical properties of Sn3X4 (X = P, As, Sb, Bi) compounds were obtained using GGA-PBE. In addition, The Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJGGA) technique was used to calculated the optoelectronic properties. The calculated electronic band structures and density of states reveal a direct band gap at Γ points varied from 0.11 eV to 1.23 eV for X = P, As, Sb, Bi. The optical absorption calculations show that all compounds have high absorption coefficients about twenty times greater than that of CuInSe2 and CdTe in the visible region. The high absorption of these materials could be attributed to the localized p-states of cation (X = P, As, Sb, Bi) in the lower region of the conduction band.