Tran-Blaha Modified Becke-Johnson Exchange Potential 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.

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.

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.

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.

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.

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.

Structural, optoelectronic and thermoelectric properties of antiperovskite compounds Ae3PbS (Ae = Ca, Sr and Ba): A first principles study

In the last years, alkaline-earth based antiperovskite compounds with small semiconductor band gap have been proven to be promising candidate for optoelectronic and thermoelectric applications. In this work, the structural, electronic, optical and thermoelectric properties of Ae3PbS (Ae = Ca, Sr and Ba) compounds have been predicted using first principles calculations based on the full-potential linearized augmented plane-wave (FP-LAPW) method and semiclassical Boltzmann transport theory. Exchange-correlation effect is treated with the generalized gradient approximation with Perdew–Burke–Ernzerhof scheme (GGA-PBE) and Tran–Blaha modified Becke–Johnson exchange potential. The lattice constant of considered materials increases as Ae goes in order from Ca to Ba and the hardness slightly decreases in this order. Ca3PbS and Sr3PbS are semiconductor with direct band gap of 0.199 eV and 0.116 eV, respectively, while Ba3PbS is nearly metallic. Important optical responses of studied antiperovskites are found in the visible and ultraviolet energy range. Finally, the thermoelectric properties including Seebeck coefficient, electrical conductivity, thermal conductivity, power factor and figure of merit are calculated. Obtained results show that Ca3PbS and Sr3PbS could be candidate for applications in thermoelectric generators at low and moderate temperatures due to their high figure of merit values.

Theoretical study of electronic structure, thermoelectric and thermodynamic properties of 2H-AgAlO2

Electronic structure of AgAlO2 have been investigated using first principles calculations based on the full-potential linearized plane-wave method as implemented in WIEN2k package. Generalized gradient approximation (PBESol) and Tran-Blaha modified Becke-Johnson exchange potential (mBJ) are adopted for the treatment of exchange-correlation effects. Calculated electronic properties show the considerable improvement of results with mBJ potential while the strong hybridization between O-2p and Ag-4d states is revealed. From the band structure obtained with mBJ potential, the thermoelectric properties are calculated using semi-classical Boltzmann transport theory. Obtained results suggest that AgAlO2 is a good thermoelectric p-type compound with figure of merit value close to unity at charge-carrier concentration about 1017 (cm−3). Finally, the thermodynamic properties including bulk modulus, isochoric and isobaric heat capacities, thermal expansion and Debye temperature of AgAlO2 also are calculated using quasi-harmonic Debye model and the obtained results are discussed in detail.

Theoretical investigations on physical properties of SrFCuCh (Ch=S and Se)

Using first principles calculations based on full-potential linearized augmented plane-wave (FP-LAPW) method, the structural, electronic and optical properties of SrFCuCh (Ch=S and Se) have been investigated. Generalized gradient approximation (GGA-PBESol) is adopted for the exchange-correlation electron interaction. Optimized structure of studied compounds are in very good agreement with experimental results. PBESol functional underestimates the electronic band gap of these materials, whereas Tran-Blaha modified Becke-Johnson exchange potential for semiconductors with band up to 7 eV (smBJ) predicts this parameter very accurately by error of just − 1.16% (for SrFCuS) and − 1.59% (for SrFCuSe) in comparison with experimental data. These reliable obtained results are used for calculating optical and thermoelectric properties including Seebeck coefficient, electrical conductivity, thermal conductivity and figure of merit. The last ones are computed with semi-classical Boltzmann theory within the constant relaxation time approximation. Our calculations show that SrFCuS and SrFCuSe as p-type compounds are promising candidate for applications in thermoelectric devices at high temperatures. Finally, the thermodynamic properties of these materials comprising bulk modulus, heat capacities, thermal expansion and Debye temperature are calculated in wide temprature range up to 1200 K at various pressures 0 GPa, 20 GPa and 50 GPa using quasi-harmonic Debye model and they are also discussed in details.

Electronic structure and thermoelectric properties of Ta-based half-Heusler compounds with 18 valence electrons

Recently, the half-Heusler compounds with 18 valence electrons have been considered as promising candidate for thermoelectric applications due to their interesting properties. In this work, the structural, electronic and thermoelectric properties of Ta-based half-Heusler TaXY (X = Ru, Rh; X = Sb, Bi, Sn and Pb) have been investigated using the full-potential linearized augmented plane-wave (FP-LAPW) method within the density functional theory (DFT) and the classical Boltzmann transport theory. Generalized gradient approximation as parameterized by Wu-Cohen (GGA-WC) and Tran-Blaha modified Becke-Johnson exchange potential (mBJ) are employed for taking on account the exchange-correlation electron potential. All four studied materials are semiconductor with indirect band gap 0.815 eV for TaRuSb, 0.906 eV for TaRuBi, 1.109 eV for TaRhSn and 1.138 eV for TaRhPb. Additionally, the spin-orbit coupling (SOC) decreases slightly the band gap of these materials. Thermoelectric properties, such as, Seebeck coefficient, electrical conductivity, power factor, total thermal conductivity and figure of merit are calculated in function of chemical potential. Obtained results show that TaXY compounds have good thermoelectric performance with high figure of merit value 0.99.

Comparative study of structural, electronic, optical and thermoelectric properties of GaS bulk and monolayer

ABSTRACTThe structural, electronic, optical properties of GaS in bulk and monolayer forms have been studied by means of full-potential linearised augmented plane wave calculations within framework of the density functional theory. Generalised gradient approximation and Tran–Blaha modified Becke–Johnson exchange potential (mBJ) were employed for the treatment of exchange-correlation effect in calculations. Our calculated lattice parameters are in good agreement with previous theoretical results and available experimental data. The negative formation enthalpy and cohesive energy indicate that both bulk and monolayer GaS can be synthesised and stabilised experimentally. Our electronic results show that the band gap of GaS monolayer is higher than that of bulk counterpart and strong hybridisation between electronic states of constituent atoms is observed in both cases. The optical properties such as reflectivity, absorption coefficient, refractive index and optical conductivity were derived from calculated complex dielectric function for wide energy range up to 35 eV. Finally, the thermoelectric properties of GaS bulk and monolayer also were calculated using semi-classical Boltzmann theory within the constant relaxation time approximation for investigating their applicability in thermoelectric devices.

SnO2 improved thermoelectric properties under compressive strain

The effect of biaxial strain on the electronic and thermoelectric properties of SnO2 is studied using state-of-the-art first-principles calculations. All calculations are based on DFT within the Tran-Blaha modified Becke-Johnson exchange potential approximation (TB-mBJ). Under biaxial compression, short covalent Sn-O bonds are formed which widen the bandgap energy as compared to that of an uncompressed SnO2. This wide bandgap results in an increase of the Seebeck coefficient enhancing therefore the electrical conductivity and consequently an improvement of the ZT figure of merit values in the range of temperature up to 400 K. In the case of a tensile strain, however, an opposite behavior is noticed all over the studied temperature range, mainly due to the resulting elongated Sn-O bonds that tend to reduce the bandgap energy value. This finding demonstrates the ability of an applied compressive strain to improve the thermoelectric efficiency of SnO2 and to favor its applicability in thermoelectric applications at room temperature and below.