Modified Becke-Johnson Exchange Potential Research Articles

First principles study of structural, electronic and optical properties of perovskites CaZrO3 and CaHfO3 in cubic phase

In this work, we present the first principles calculations for structural, electronic and optical properties of perovskites CaZrO3 and CaHfO3 using the full-potential linearized augmented plane wave method (FP-LAPW) within the framework of density functional theory (DFT) as implemented in WIEN2k package. The exchange-correlation potential is treated with local density approximation (LDA) and generalized gradient approximation (GGA-PBE and PBESol). Additionally, the Tran Blaha modified Becke-Johnson exchange potential (mBJ) also is employed for electronic and optical calculations due to that it gives very accurate band gap of solids. Our obtained structural parameters are in good agreement with experimental datas and other theoretical results. The energy band gap obtained with mBJ is 4.56 eV for CaZrO3 and 5.27 eV for CaHfO3. The hybridization of states of O atom with those of Zr and Hf atoms in CaZrO3 and CaHfO3, respectively, is observed. The spin-orbit coupling effect on electronic properties of considered compounds also is investigated. Finally, the linear optical properties of CaZrO3 and CaHfO3 are derived from their complex dielectric function calculated with mBJ potential for wide energy range up to 45 eV, and all of them analyzed in details.

Assessing the performance of the Tran–Blaha modified Becke–Johnson exchange potential for optical constants of semiconductors in the ultraviolet–visible light region

We report on the performance of density functional theory (DFT) with the Tran–Blaha modified Becke–Johnson exchange potential and the random phase approximation dielectric function for optical constants of semiconductors in the ultraviolet–visible (UV-Vis) light region. We calculate optical bandgaps Eg, refractive indices n, and extinction coefficients k of 70 semiconductors listed in the Handbook of Optical Constants of Solids [(Academic Press, 1985), Vol. 1; (Academic Press, 1991), Vol. 2; and (Academic Press, 1998), Vol. 3] and compare the results with experimental values. The results show that the calculated bandgaps and optical constants agree well with the experimental values to within 0.440 eV for Eg, 0.246–0.299 for n, and 0.207–0.598 for k in root mean squared error (RMSE). The small values of the RMSEs indicate that the optical constants of semiconductors in the UV-Vis region can be quantitatively predicted even by a low-cost DFT calculation of this type.

Electronic, electrical and optical properties of Ag doped CuO through modified Becke-Johnson exchange potential

This study examined the influence of the Ag doping concentration on the structural, electrical and optical properties of copper oxide (CuO), using the density functional theory DFT with Tran-Blaha modified Becke-Johnson (mBJ). Based on the optimized structural parameters, the structural properties, the band gaps, density of states (DOS), the profiles of the optical spectra and optical properties, including the real and imaginary parts of dielectric function, absorption coefficient, reflectivity and refractive index are obtained and showed a good agreement with experimental results. Beside this, our results indicate that CuO is an antiferromagnetic semiconductor material with an indirect gap about 1.99 eV. This increasing with decreasing Silver concentration. Furthermore, the absorption spectra display excellent physical behavior in the range of visible light which it is in good with agreement with many experimental data. In fact, this confirms the physical characteristics that can present CuO to be used as suitable absorbent material in solar cells.

Electronic, optical and thermoelectric properties of SnGa2GeX6 (X = S, Se) compounds

Electronic, optical and thermo-electric properties of two quaternary chalcogenides SnGa2GeX6 (X = S, Se) have been studied by using density functional theory. Modified Becke-Johnson exchange potential (mBJ-GGA) was used to calculate the band gaps of these compounds. Both compounds show pseudo direct band gap of 1.74 and 1.24 eV for SnGa2GeS6 and SnGa2GeSe6, respectively. The band gap decreases when replacing the X cations from S to Se. The optical properties such as dielectric function, energy loss function, extension coefficient, refractive index, and reflectivity of these compounds are discussed in details. The thermo-electric properties are studied using Boltzmann statistics through BoltzTrap code. High absorption peaks and figure of merits (ZT) for both compounds reveal that they are good candidates for the optoelectronics and thermo-electric devices.

Electronic and optical properties of 2H-perovskite related tantalum/niobium oxides

Quasi-one-dimensional oxides [Formula: see text] (A = Ba, Sr; [Formula: see text] = Na, Li and B = Ta, Nb) have been synthesized and found to display efficient photoluminescence. Their electronic and optical properties are calculated by using first-principles calculations. The modified Becke–Johnson exchange potential has been used to obtain accurate band gap. Our results reveal that alkali metal and alkaline-earth metal ions have very small contribution to the states around Fermi level, and for these compounds, the top valence bands and the conduction band bottom are dominated by O-2p and Nb/Ta-d states, respectively. All of these compounds have indirect band gap, with valence band maximum at K point and conduction band minimum at [Formula: see text] point. Optical absorption spectrum is characterized by two prominent peaks. The lower energy peak originates from electron transitions between Ta/Nb-[Formula: see text] and O-2p states, while the higher energy peak is determined by electron transitions between Ta/Nb-[Formula: see text] and O-2p. Despite the one-dimensional feature of the lattice structure, the electronic band structure and optical properties show three-dimensional character. We find that the band gap and optical absorption threshold are considerably larger than the energy of excitation light in the luminescence measurement. This indicates the important role of the in-gap states, which may be induced by the impurity or vacancy.

Comment on “DFT investigation of structural, electronic and optical properties of pure and Er-doped ZnO: Modified Becke-Johnson exchange potential”

Recently, Alkahtani et al. [1] studied the structural, electronic and optical properties of pure ZnO and Er-doped ZnO using generalized gradient approximation plus modified Becke-Johnson exchange potential. They doped erbium (Er) atom to ZnO zinc-blende structure. They did not perform spin polarized calculations, so their obtained electronic and optical properties are wrong. Also, the intra-band transition has not been considered in the their optical investigations. The correct form of these properties is presented and discussed in this paper.

Investigation of the Perovskite KSrX3 (X = Cl and F) Compounds, Examining the Optical, Elastic, Electronic and Structural Properties: FP-LAPW Study

The optical and electronic density of states (DOS) and elastic and structural properties of crystalline perovskites KSrX3 (X = Cl and F) are examined using the full potential linearized augmented plane wave (FP-LAPW) technique in the context of the Perdew, Burke and Ernzerhof’s (PBE) generalized gradient approximation (GGA), the local density approximation (LDA) and the modified Becke-Johnson exchange potential (mBJ-GGA), while the structural properties of the KSrX3 are calculated using LDA, GGA and Wu-Cohen (WC) functionals. Our findings are that the KSrF3 compound has a direct energy band gap (E g) at (Γ–Γ) with 5.54 eV, 5.42 eV, and 10.35 eV using PBE-GGA, LDA and mBJ-GGA approximations, respectively. The KSrCl3 compound also has an indirect energy band gap (M–Γ) with 4.45 eV, 4.3 eV, and 7.88 eV, as discovered using PBE-GGA, LDA and mBJ-GGA approximations, respectively. The coefficient of extinction, index of refraction, dielectric function and the fountains of apex of the optical spectra are examined with regard to the computed electronic structure.

Magneto-electronic, thermal, and thermoelectric properties of some Co-based quaternary alloys

In this study, quaternary Heusler alloys CoFeCrZ (Z = Si, As, Sb) were investigated based on the modified Becke–Johnson exchange potential. The electronic structures demonstrated that CoFeCrZ (Z = Si, As, Sb) alloys are completely spin polarized with indirect bandgap and has an integer magnetic moment according to the Slater–Pauling rule. Pugh's and Poisson's ratios showed that these materials are highly ductile with high melting temperatures. The thermal properties comprising the thermal expansion coefficient, heat capacity, and Grüneisen parameter were evaluated at various pressures from 0 to 20 GPa. The Grüneisen parameter values indicated the strong anharmonicity of the lattice vibrations that predominated in these compounds. We also studied the dependency of the thermoelectric transport properties on the temperature, i.e., the thermal conductivity and Seebeck coefficient. These alloys exhibited low lattice thermal conductivity and good Seebeck coefficients at room temperature. The half-metallic structures of these compounds with large band gaps and adequate Seebeck coefficients mean that they are suitable for use in spintronic and thermoelectric device applications.

Excitonic effects on the optical response of monolayer and bilayer graphene-like silicon carbide

The graphene-like silicon carbide (SiC) has attracted much attention recently owing to its potential application in optoelectric devices. In this work, we have theoretically investigated the excitonic effects on the dielectric constants [ε(ω)] of monolayer (ML-) and bilayer (BL-) SiC using the first principle calculations with solving the Bethe-Salpeter equation. The Tran-Blaha modified Becke-Johnson exchange potential combined with the Perdew and Wang correlation potential is used to overcome the underestimate of bandgap. Within the independent particle approximation, BL-SiC not only has the same intralayer π→π∗ transition in the transverse ε(ω) as ML-SiC but also has an interlayer π→π∗ transition in the longitudinal ε(ω). The excitonic effects dramatically change the absorption spectra of two polarization directions (transverse and longitudinal). For the transverse ε(ω), BL-SiC has a similar excitonic absorption profile to ML-SiC but shows a blue-shift relative to ML-SiC and an apparent decrease in the binding energy of bright exciton. For the longitudinal ε(ω), ML-SiC has a bright exciton with a large binding energy of 1.87eV related to the σ→π∗ transition band, and BL-SiC has a bright exciton with a small binding energy of 0.41eV related to the interlayer π→π∗ transition.

A DFT Study on Structural, Electronic Mechanical and Thermodynamic Properties of 5f-Electron System BaAmO3

The structural, electronic, mechanical and thermodynamic properties of the perovskite oxide BaAmO3 have been predicted using the full-potential linearized augmented plane wave (FP-LAPW) method. The equilibrium lattice constant, bulk modulus and pressure derivative were computed using different exchange correlations. The optimization of structure was carried out in ferromagnetic, anti-ferromagnetic and non-magnetic states, and the compound was found to be stable in the ferromagnetic state. A systematic study on the band structure and density of states was accomplished using generalized gradient approximation (GGA), Hubbard approximation (GGA + U) and modified Becke–Johnson exchange potential (mBJ),and the compound was found to have a half-metallic nature in all the approximations. The calculated total spin magnetic moment was found to be 5 μ B in all the approximations used. The second-order elastic constants, Young modulus, shear modulus, Poisson ratio and anisotropic factor have also been calculated. In order to have a complete understanding of BaAmO3, the thermodynamic properties were studied in the pressure range of 0 to 40 GPa and the temperature range extending from 0 to 600 K.

Effect of Fe Doping on Magnetic Properties and Lattice Structure of Ferromagnetic EuO

The structural, electronic, and magnetic properties of Fe-doped EuO (Eu0.75Fe0.25O, Eu0.50Fe0.50O, and Eu0.25Fe0.75O) in the rock salt ferromagnetic phase have been studied. Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) was used for structural analysis of these compounds. The lattice constant linearly decreased with increase in doping concentration of Fe atoms. Spin-polarized calculations were carried out using the modified Becke-Johnson exchange potential with Hubbard U correction (mBJ + U method). Semiconductor EuO showed a metallic character when doped with Fe atoms. The calculated density of states (DOS) of Eu0.75Fe0.25O, Eu0.50Fe0.50O, and Eu0.25Fe0.75O exhibit extra peaks of Fe atom 3 d states in the valance band between −10 and 3.5 eV. With an increase in Fe doping, the band gap was decreased due to an increase in spd exchange interaction between the band electrons and localized 3d electrons of transition atoms. Moreover, the properties of the doped EuO were found to be dependent on the location of dopant atoms.

First-principles identification of charge-transition levels of native defects in BaF2

This paper reports on semilocal and hybrid density functional analysis of charge-transition levels of native defects in BaF2 structure. The transition level is defined as the Fermi level where two defect charge states have the same formation energy. The errors arising from the small supercell size effects have been relieved through extrapolating the formation energies to the limit of infinite supercell size. The level placement in the corrected band gap is achieved using a correction factor obtained from the difference between the valence band maxima in semilocal and hybrid calculations. The band gap size from hybrid calculation is validated using the full-potential, linearized augmented planewave method with the modified Becke–Johnson exchange potential. Our results are sufficiently accurate and, thus, significant for direct comparison with experiments.

Structural, electronic, optical and thermoelectric properties of Mg3X2 (X = N, P, As, Sb, Bi) compounds

Magnesium pnictides Mg3X2 (X=N, P, As, Sb, Bi) have gained importance due to their fascinating physical properties. These compounds have been mainly studied from the structural and electronic band structure aspects. In this work, the structural, electronic, optical and thermoelectric properties of Mg3X2 (X=N, P, As, Sb, Bi) compounds have been investigated by using density functional theory. The crystal structure of the compounds is optimized through Wu-Cohen generalized gradient approximation (WC-GGA). Modified Becke-Johnson exchange potential predicted the bandgaps larger than the WC-GGA and Englo-Vosko GGA. All the compounds are predicted to be direct bandgap. Bandgap of the compounds decreased by changing the cation from N to Bi. Optical properties of the compounds are described in details. The thermoelectric properties of the compounds are also characterized. On the basis of suitable direct bandgap nature and good thermoelectric coefficients these materials are potential candidates for the optoelectronics and thermoelectric applications.

The optoelectronic properties of a solar energy material: Ag2HgSnS4

We used an ab initio full potential-linearized augmented plane wave technique within the density functional theory to study the structural and optoelectronic properties of Ag2HgSnS4 in a wurtzite-stannite phase. The exchange correlation effects are included through the generalized gradient approximation and modified Becke-Johnson exchange potential. Various physical quantities, such as lattice parameter, bulk modulus, band structure and density of states, are given. Also, we have presented the results of the effective mass for the electrons in the CB and the holes in the BV. We show that the modified Becke-Johnson exchange potential can predict the energy band gap in better agreement with the experiment. In addition the dielectric function and energy-loss function are presented for the energy range of 0-26 eV. The electronic and optical properties indicate that this compound can be successfully used in optoelectronic devices

Investigation of opto-electronic properties of ZnS polymorphs through modified Becke-Johnson exchange potential

The structural, electronic and optical properties of ZnS polymorphs are studied systematically based on Density Functional Theory (DFT). A competition between the Rocksalt (B1), zinc-blende (B3) and wurtzite (B4) as the ground state phase is found depending on whether LDA (Local Density Approximation) or GGA (Generalized Gradient Approximation) is used. In both approximations, we have investigated within Gibbs free energies, the transition pressures of (B3) and (B4) phases to (B1) structure. To calculate the electronic and optical properties of (B3) and (B4) phases of ZnS, the exchange-correlation potential is treated with two approximations, and we have found that the newly modified Becke-Johnson (mBJ) functional, significantly improves the band gap energies. We have predicted a direct band gap for the both phases of the material of interest. Moreover, the densities of states for the two polymorphs are also presented. Additionally, the dielectric function and other parameters are calculated for discussing the optical properties of ZnS. The comparison of the calculated energy band gaps with the available experimental data is indicated that the mBJ provides a better description of the electronic properties of ZnS than the standard approach. Our results are consistent with the literature data.

DFT investigation of structural, electronic and optical properties of pure and Er-doped ZnO: Modified Becke-Johnson exchange potential

The structural, electronic and optical properties of pure ZnO and Er-doped ZnO are investigated by density functional theory (DFT) with generalized gradient approximation plus modified Becke-Johnson exchange potential (GGA+mBJ). The obtained results of electronic and optical properties were improved. Good agreement with the experimental and theoretical studies is obtained for pure ZnO since the results of Er-doped ZnO in zinc blend structure are considered as new predictions. The energy gap value of Er-doped ZnO is found to increase with Erbium incorporation, affecting the absorption coefficients in all spectra regions. Red shift is also achieved under Er doping indicating the importance of its 4f donor occupied states. Similar behavior is observed in the literature for Er-doped ZnO in wurtzite structure.

Electronic, optical and elastic properties of cubic perovskite CsPbI3: Using first principles study

Structural stability and also elastic, electronic, and optical properties of cubic perovskite CsPbI3 are calculated using the full-potential linearized augmented plane wave method (FP-LAPW) based on density functional theory (DFT). The exchange-correlation potential is evaluated using the local density approximation (LDA), generalized gradient approximation (GGA) and coupling it with modified Becke-Johnson exchange potential (mbj-GGA). The calculated structural properties such as equilibrium lattice constant, the bulk modulus and its pressure derivative are in good agreement with the available data. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young's modulus and Poisson's ratio are calculated as well. The calculations of electronic band structure and density of states demonstrate that this compound has a direct energy band gap in R symmetry point about 1.56eV and 1.879eV by GGA and mbj-GGA respectively. The optical diagrams such as the real and imaginary parts of dielectric function, absorption, refractive index and electron energy loss, in different pressure, are calculated in [0–15eV] energy range.

Potential thermoelectric material : a first-principles study

The electronic structures and thermoelectric properties of are investigated by first-principles calculations and semiclassical Boltzmann transport theory. Both electron and phonon transport are considered to attain the figure of merit ZT. A modified Becke–Johnson exchange potential, including spin–orbit coupling (SOC), is employed to investigate the electron part of . It is found that SOC has an obvious effect on valence bands, producing huge spin–orbital splitting, which leads to a remarkable detrimental effect on the p-type power factor. However, SOC has negligible influence on conduction bands, so the n-type power factor hardly changes. The temperature dependence of lattice thermal conductivity by assuming an inverse temperature dependence is attained from a reported ultralow lattice thermal conductivity of 0.31 at room temperature. Calculating scattering time τ is challenging, but a hypothetical τ can be adopted to estimate thermoelectric conversion efficiency. The maximal figure of merit ZT is up to about 0.70 and 0.60 with scattering time τ = 10−14 s and τ = 10−15 s, respectively. These results convince us that may be an efficient thermoelectric material for real devices.

Investigating the Structural, Thermal, and Electronic Properties of the Zircon-Type ZrSiO4, ZrGeO4 and HfSiO4 Compounds

In the present study, the structural, thermal, and electronic properties of some important orthosilicate dielectrics, such as the ZrSiO4, ZrGeO4, and HfSiO4 compounds, have been investigated theoretically with the use of first-principle calculations. We attribute the application of the modified Becke–Johnson exchange potential, which is basically an improvement over the local density approximation and the Perdew–Burke–Ernzerhof exchange–correlation functional, for a better description of the band gaps of the compounds. This resulted in a good agreement with our estimated values in comparison with the reported experimental data, specifically for the ZrSiO4, and HfSiO4 compounds. Conversely, for the ZrGeO4 compound, the calculated electronic band structure shows a direct band gap at the Γ point with the value of 5.79 eV. Furthermore, our evaluated thermal properties that are calculated by using the quasi-harmonic Debye model indicated that the volume variation with temperature is higher in the ZrGeO4 compound as compared to both the ZrSiO4 and HfSiO4 compounds, which is ascribed to the difference between the electron shells of the Si and Ge atoms. Therefore, these results also indicate that while the entropy (S) and enthalpy (U) parameters increase monotonically, the free energy (G), in contrast, decreases monotonically with increasing temperature, respectively. Moreover, the pressure and temperature dependencies of the Debye temperature Θ, thermal expansion coefficient, and heat capacities CV were also predicted in our study.

Native defects as sources of optical transitions in MgAl2O4 spinel

The outstanding physical and chemical properties of the magnesium aluminate (MgAl2O4) spinel makes it an important material for novel technological applications. Considering that a presence of native defects can promote important changes in those properties, in this work we present a study of the structural, electronic and thermodynamic properties of the MgAl2O4 spinel. The calculated formation energy for isolated defects, such as the vacancies of magnesium (VMg), aluminum (VAl) and oxygen (VO), oxygen interstitial (Oi), magnesium and aluminum antisites (MgAl, AlMg), as well as some complex defects (VO + Oi, VO + AlMg, VO + MgAl, MgAl + AlMg) in the most stable charge states are shown. Through experimental data, we obtained that complex defects centers, such as VO, VO + Oi, VO + AlMg and VO + MgAl at different charge states are good candidates for the observed optical transitions at 4.75, 5.3, and 6.4 eV. Our findings were obtained from ab initio electronic structure calculations performed by using density functional theory. The Perdew–Burke–Ernzerhof generalized gradient approximation was used for the exchange-correlation potential. Furthermore, a modified Becke-Johnson exchange potential (GGA-mBJ) correction to the exchange potential were used to obtain a suitable value for the band gap energy, 7.40 eV, in accordance with the experimental one of 7.8 eV.