Modified Becke-Johnson Exchange Potential Research Articles

First Principles Investigation of the Elastic, Optoelectronic and Thermal Properties of XRuSb: (X = V, Nb, Ta) Semi-Heusler Compounds Using the mBJ Exchange Potential

Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke–Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants (Cij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. 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 semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.

Electronic Structure of YbB_{6}: Is it a Topological Insulator or Not?

To finally resolve the controversial issue of whether or not the electronic structure of YbB_{6} is nontrivially topological, we have made a combined study using angle-resolved photoemission spectroscopy (ARPES) of the nonpolar (110) surface and density functional theory (DFT). The flat-band conditions of the (110) ARPES avoid the strong band bending effects of the polar (001) surface and definitively show that YbB_{6} has a topologically trivial B 2p-Yb 5d semiconductor band gap of ∼0.3 eV. Accurate determination of the low energy band topology in DFT requires the use of a modified Becke-Johnson exchange potential incorporating spin-orbit coupling and an on-site Yb 4f Coulomb interaction U as large as 7eV. The DFT result, confirmed by a more precise GW band calculation, is similar to that of a small gap non-Kondo nontopological semiconductor. Additionally, the pressure-dependent electronic structure of YbB_{6} is investigated theoretically and found to transform into a p-d overlap semimetal with small Yb mixed valency.

Ab initio study of structural, electronic and optical properties of ternary chalcopyrite semiconductors

In this paper, structural, electrical and optical properties of AgGaX2 (X=S, Se, Te) were studied by using Full Potential Linear Augmented Plane Wave (FP-LAPW) based on density functional theory. Perdew Becke Ernzerhof (GGA-PBE) and Wu Cohen Generalized gradient approximation (GGA-Wc), Engel Voskov Generalized Gradient Approximation (EV) and modified Becke-Johnson exchange potential (MBJ) were used for the exchange correlation potential. GGA-PBE was closed to the other and experimental data for lattice constant, bulk modulus (B) and its first derivative (B′), and MBJ potential was in good agreement with the experiment and other calculations for band gap energy and the optical properties. Band structure, total and partial density of states were plotted to obtain electronic properties and the band gap was direct for all components. By using imaginary and real part of dielectric functions, some optical properties such as reflection coefficient (R), refractive index (n), extinction coefficient (k) were obtained and the role of X atoms (X=S, Se, Te) in optical properties were investigated.

High efficiency of transmittance and electrical conductivity of V doped ZnO used in solar cells applications

The full-potential linearized augmented plane wave method (FP-LAPW) based on the density functional theory (DFT) and Boltzmann's Transport theory, are employed to investigate theoretically the electronic structure, optical and electrical properties of vanadium -doped wurtzite ZnO with different concentrations (3.125%, 6.25%, 12.5%, 25%). The FP-LAPW based on the new potential approximation known as the Tran-Blaha modified Becke–Johnson exchange potential approximation (mBJ) was also applied with the primary goal of improving the electronic structure description specially the band gap energy. The calculated band structure and density of states (DOS) exhibit a band gap of pure ZnO (3.3 eV) closer to the experimental one. As well, our results indicate that the average transmittance in the 400–1000 nm wavelength region was 93%. We found that Zn96.875V3.125O is the optimized composition of the V doped ZnO, which has the highest conductivity (3.2 × 103 (Ωcm)−1) and transmittance. The high transmittance and electrical conductivity indicate that hexagonal V:ZnO system is a potential as material for solar energy applications.

Half‐Heusler compounds with a 1 eV (1.7 eV) direct band gap, lattice‐matched to GaAs (Si), for solar cell application: A first‐principles study

AbstractA systematic theoretical study of the structural and electronic properties of new half‐Heusler compounds is performed to find the appropriate target key physical parameters for photovoltaic application. As a result, five ternary half‐Heusler compounds ScAgC, YCuC, CaZnC, NaAgO, and LiCuS are studied by density functional theory for potential applications in multi‐junction solar cells. The calculated formation enthalpies indicate that these materials are thermodynamically stable. Using state‐of‐the‐art modified Becke–Johnson exchange potential approximation, we find a direct band gap close to 1 eV (1.88 eV) for ScAgC, YCuC, CaZnC, NaAgO (LiCuS) being quasi‐lattice matched to GaAs (Si). In addition, the band offsets between half‐Heusler compounds and GaAs (Si) and their consequences for heterostructures are derived using the modified Tersoff method for the branch‐point energy. Furthermore, the elastic constants and phonon dispersion curves are calculated. They indicate the respective mechanical and dynamical stability of these half‐Heusler compounds.

Modified Becke-Johnson exchange potential: improved modeling of lead halides for solar cell applications

We report first-principles calculations, within density functional theory, on the lead halide compounds PbCl 2 , PbBr 2 , and CH 3 NH 3 PbBr 3−x Clx, taking into account spin-orbit coupling. We show that, when the modified Becke-Johnson exchange potential is used with a suitable choice of defining parameters, excellent agreement between calculations and experiment is obtained. The computational model is then used to study the effect of replacing the methylammonium cation in CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 with either N 2 H 5 + or N 2 H 3 + , which have slightly smaller ionic radii than methylammonium. We predict that a considerable downshift in the values of the band gaps occurs with this replacement. The resulting compounds would extend optical absorption down to the near-infrared region, creating excellent light harvesters for solar cells.

First principle study of vanadium doped ZnS: Structural, electronic, elastic, magnetic and optical properties using mBJ approximation

The structural, electronic, magnetic, mechanical and optical properties of ternary Zn1−xVxS (x = 0.0, 0.25, 0.50, 0.75 and 1.0) ferromagnetic semiconductor alloys have been studied in the zinc blende (ZB) phase, by first principle approach. Density functional theory has been employed to calculate the fundamental properties of the alloys using full-potential linearized augmented plane-wave plus the local orbitals (FP-LAPW + Lo) method. In addition, the electronic and magnetic properties are investigated by the local spin density approximation coupled with the modified Becke–Johnson exchange potential (mBJLDA). Structural analysis revealed that the structure of the three alloys Zn0.75V0.25S, Zn0.50V0.50S, and Zn0.25V0.75S are stable in the ferromagnetic phase. It is noted that the calculated lattice constant decreases, while the bulk modulus increases with the increase of V content. The density of states and spin polarized band structure investigation demonstrated the half-metallic ferromagnetic characteristics of the investigated alloys and are also used to determines p–d exchange constants N0α and N0β, due to S (p)–V(3d) hybridization. These results reveal that magnetic moment of V dopant element reduced from its free space value of 3 μB, because the Zn and S sites acquire minor atomic magnetic moments. The energy band gap analysis show an increasing trend with V doping that makes our compound a suitable candidate for the fabrication of devices operating in the ultraviolet region. Moreover, the static dielectric constant, ε1 (ω), and static refractive index, n (ω), increases with V contents. The incorporation of V generates some new peaks in the energy regions of 0–2.83 eV and 4–10 eV. The substitution by V increases the intensity of the peaks, and a slight red shift has been observed in the absorption peak. The extinction coefficient k (ω) and optical conductivity also follow a similar trend to that of the dielectric constants. These results give deep insight into the design of devices for optical and spintronics applications using V doped ZnS.

First-principles energy band calculation of Ruddlesden–Popper compound Sr3Sn2O7 using modified Becke–Johnson exchange potential

The electronic structure of Sr3Sn2O7 is evaluated by the scalar-relativistic full potential linearized augmented plane wave (FLAPW+lo) method using the modified Becke–Johnson potential (Tran–Blaha potential) combined with the local density approximation correlation (MBJ–LDA). The fundamental gap between the valence band (VB) and conduction band (CB) is estimated to be 3.96eV, which is close to the experimental value. Sn 5s states and Sr 4d states are predominant in the lower and upper CB, respectively. On the other hand, the lower VB is mainly composed of Sn 5s, 5p, and O 2p states, while the upper VB mainly consists of O 2p states. These features of the DOS are well reflected by the optical transition between the upper VB and lower CB, as seen in the energy dependence of the dielectric function. Furthermore, the absorption coefficient estimated from the MBJ–LDA is similar to the experimental result.

Optical conductivity enhancement and band gap opening with silicon doped graphene

The linear optical and electronic properties of a monolayer graphene sheet are investigated using the Density Functional Theory within the Full Potential Linearized Augmented Plane Wave (FP-LAPW) formalism. Three approaches are used in this work: The Generalized Gradient Approximation (GGA), the Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ); implemented in WIEN2K code; and GW (Green function G and screened Coulomb interaction W) implemented in Yambo code.The band gap of graphene with and without silicon doping and the effect of silicon on optical properties of graphene are calculated. The silicon doping opens the band gap of graphene and increases its optical conductivity. This material may be used in solar cell application. Other optical properties such as reflectivity and refractive index are also studied.

Electronic structure and optical properties of Cu3PX4(X=S and Se): Solar cell made of abundant materials

The electronic structure and optical properties of Cu3PX4 (X=S and Se) have been investigated employing the full potential linearized augmented plane wave (FP-LAPW) method. The modified Becke–Johnson exchange potential (TB-mBJ) was used along with the generalized gradient approximation proposed by of Perdew–Burke–Ernzerhof (GGA-PBE) to treat the exchange-correlation contribution. Our results are found to be exceptionally in good agreement with exciting theoretical and experimental data. The calculated band structure shows a direct band gap of 1.376eV for Cu3PSe4 and an indirect band gap of 1.87eV for Cu3PSe4. The band gap dependent on optical properties such as dielectric function and absorption coefficient are predicted within this study. The optical responses suggest that Cu3PSe4 is promising as a photovoltaic material thanks to its high absorption coefficient and photoconductivity in the visible light.

Theoretical investigation of spontaneous polarization, electronic and optical properties of cubic perovskite BaHfO3

Electronic, optical properties and spontaneous polarization of cubic perovskite BaHfO3 have been investigated using the Full Potential Linear Augmented Plane Wave method, implemented in the Wien2k code, in connection with the Generalized Gradient Approximation (GGA) and the Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ). The calculation of band structure and density of state using TB-mBJ approach shows that the gap of BaHfO3 is direct and equal to 5.9 eV which is in good agreement with the experiment data (6.0 eV), compared with GGA which gives 3.9 eV. The absorption coefficient α (ω) and the complex dielectric function e (ω) are also investigated and predict that this compound can be effectively used in UV based optoelectronic devices. Furthermore, Using the PI approach, we can calculate the spontaneous polarization which is equal to 0.40 C/m2 and predict that is in the same order as the Ps of other perovskite.

Comparative study between TB-mBJ and GGA+U on magnetic and optical properties of CdFe2O4

Full Potential Linearized Augmented Plane Wave (FP-LAPW) based on density functional theory (DFT) is carried out to study the density of states, optical properties and XMCD properties of bulk spinel ferrite CdFe2O4. The exchange correlation potential was solved by Generalized Gradient Approximation (GGA) that underestimates the band gap value, therefore, the later needed to be corrected using two approaches: Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ) and GGA plus the multi-orbital mean-field Hubbard potential (GGA+U). These methods provide accurate results in good agreement for the optical properties and band gap with experimental data.CdFe2O4 has a coefficient of absorption more than 104/cm in the visible range. The first critical point known as optical absorption edge calculated with GGA+U and TB-mBJ appears at 1.56eV and 1.88eV, respectively.The XMCD spectra show a double pic in L3 edge indicating the presence of both Fe2+ and Fe3+ ions, occupying the octahedral sites. However, using GGA+U the charge of the atoms is well localized and subsequently the double peak does not reproduce.The crystal field creates additional levels that provide radiation in the visible, having these properties; this compound promotes its use for device applications operating over a wide energy range based on CdFe2O4 in optoelectronics.

Structural, bonding, and electronic properties of the hexagonal ferroelectric and paraelectric phases of LuMnO3 compound: a density functional theory study.

We have investigated the structural, bonding, and electronic properties of both ferroelectric (FE) and paraelectric (PE) phases of the hexagonal LuMnO3 compound using calculations based on density functional theory. The structural properties have been determined by employing the generalized gradient approximation with Perdew-Burke-Ernzerhof and Wu-Cohen parameterization. The bonding and electronic properties have been treated by recently developed modified Becke-Johnson exchange potential, which succeeded to open a band gap for both PE and FE phases, in agreement with experimental predictions. The Bader's topological analysis of electronic density showed that the character of the Lu-O axial bonds changes when the crystal exhibits the PE → FE structural transition. This fact is in agreement with experimental findings. The covalent character of the Lu-O bond significantly increases due to orbital hybridization between the Lu 5dz(2) and O 2pz-states. This bonding mechanism causes the ferroelectricity in the hexagonal LuMnO3 compound.

Strain effects on the electronic structure of ZnSnP2 via modified Becke–Johnson exchange potential

ZnSnP 2 is a promising photovoltaic absorber material with a direct band gap of 1.68 eV, further reducing the band gap of ZnSnP 2 that can achieve higher photovoltaic conversion efficiency. To achieve this target, the influence of biaxial in-plane strain (±3%) on the band gap, hole effective mass and optical properties of ZnSnP 2 were investigated by first-principles calculations via Modified Becke–Johnson exchange potential. The results indicate that the biaxial tensile strain can reduce the band gap of ZnSnP 2 from 1.3 eV to 1.0 eV and enhance the absorption of visible light of c -axis direction, while the biaxial compress strain increases the band gap of ZnSnP 2 slightly. This research provides an alternative approach to tune the band gap of ZnSnP 2 by strains. The variation of the band gap under different strains is determined by the highest-energy valance band state, and it can be explained by the redistribution of electrons under different strain. • The influence of biaxial in-plane strain (±3%) on the band gap of ZnSnP 2 were investigated by DFT calculations. • MBJ exchange potential can describe the band structure of ZnSnP 2 quite well. • Tensile strain brings a substantial decrease of the band gap, while the compress strain has no evident effect. • The calculated visible light adsorption coefficient increases along c -axis direction under tensile strain.

Structural, electronic and nonlinear optical properties of B3 and B20 compounds: A first-principles investigation within the LDA, GGA and modified Becke–Johnson exchange potential plus LDA

The structural, electronic, and nonlinear optical properties of 111 crystals belonging to structural types B3 (84 crystals) and B20 (27 crystals) have been investigated by first-principles calculations using the full-potential linearized augmented plane wave (FP-LAPW) method in the framework of density functional theory. Calculations of the electronic band structure and nonlinear optical properties were performed using local-density approximation (LDA), generalized gradient approximation (GGA), and a combination of modified Becke—Johnson exchange potential plus LDA (mBJ+LDA) for exchange–correlation potential. Equilibrium lattice constant a0, bulk modulus B0, first pressure derivative B′ of the bulk modulus, band gaps Eg, and second-order nonlinear susceptibility tensor components |χ123| at 0eV and at 1.064 and 10.6μm wavelengths are presented. The obtained results are compared to available experimental and theoretical (computational) data. A correlation between the |χ123| tensor component data arrays and the distributions of crystal structures with respect to their degree of pseudoinversion is analyzed.

Band‐gap and phonon distribution in alkali halides

A systematic first‐principles study is performed to calculate the structural, electronic, dynamical, and thermodynamic properties of alkali halides NaF, NaCl, NaBr, and NaI by means of both full‐potential linear augmented plane‐wave, and plane wave pseudopotential methods. The obtained structural parameters agree favourably with experimental findings. The calculated band gaps are underestimated by GGA functional compared to experiment. The gap values are improved from the modified Becke–Johnson exchange potential, which gives band gaps in perfect agreement with the measured values. In addition, linear‐response approach to the density functional theory is used to derive several quantities such as the Born effective charges, high‐frequency dielectric constant, phonon band structure, and phonon density of states. The dynamical properties of Na‐based alkali halides are also analysed and discussed. Finally the temperature dependence of various quantities such as the mean‐squared displacement, and the heat capacity are computed using the quasi‐harmonic approximation.

Density functional study of the Ge(111)c(2 × 8) surface using the modified Becke-Johnson exchange potential with LDA correlation and spin–orbit interactions

We show that the MBJLDA exchange and correlation potential proposed by Tran and Blaha for bulk materials [Phys. Rev. Lett. 2009, 102, 226401], combined with spin-orbit interactions and LDA pseudopotentials within the plane wave density functional method, accurately reproduces the electronic structure and photoemission data of the complex Ge(111)c(2 × 8) surface without requiring any energy shifts. The MBJLDA + SO calculations also enable the nature of the states comprising the various photoemission bands to be unambiguously determined. Coupled with earlier studies, these results indicate that this new approach provides an accurate and computationally viable method for investigating semiconductor surfaces.

Optoelectronic response of spinels CdX2O4 with X = (Al, Ga, In) through the modified Becke–Johnson functional

Structural, electronic, and optical properties of CdAl2O4, CdGa2O4, and CdIn2O4 are investigated using the first principles technique based on the new potential approximation known as the Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ). We discuss the improvements in the band gap determination using TB-mBJ compared to the standard generalized gradient approximation in density functional theory. The calculated equilibrium lattice parameters are in reasonable agreement with the experimental results. Electronic properties have been studied through the calculation of band structure and density of states. Based on our electronic structure obtained using the mBJ method, we have calculated various optical properties, including the complex dielectric function ε(ω), complex index of refraction n(ω), reflectivity coefficient R(ω), absorption coefficient α(ω), and the electron energy-loss function L(ω) as functions of the photon energy. We chose these three representative oxides spinel due to their potential applications in optoelectronics and optical fields.

Structural, electronic, and optical properties of orthorhombic and triclinic BiNbO4 determined via DFT calculations

We performed ab initio calculations using the FPLAW method with the local density approximation (LDA) implemented in the WIEN2 k code for the orthorhombic (α) and triclinic (β) phases of BiNbO4. The modified Becke–Johnson exchange potential (mBJ)-LDA approach was also used to improve the electronic properties. The lattice constants calculated for both structures using the LDA are in good agreement with the experimental values. For the band structure calculations, the mBJ-LDA approach provides reasonable agreement for the band gap value compared with the LDA. The estimated (mBJ)-LDA band gap values are 2.89 eV (3.73 eV) and 2.62 eV (3.15 eV) for the α and β phases of BiNbO4, respectively. Significant optical anisotropy is clearly observed in the visible-light region. We also calculated and evaluated the electron energy loss spectrum for BiNbO4. This work provides the first quantitative theoretical prediction of optical properties and electron energy loss spectra for both the orthorhombic and triclinic phases of BiNbO4.

Electronic structure of Eu2+-doped SrAl2O4 using modified Becke–Johnson exchange potential

The optimized electronic structure of Eu2+-doped SrAl2O4 is calculated by using the modified Becke–Johnson potential combined with the local density approximation. The calculated minimum energy gap of SrAl2O4 is 6.9eV, which is close to the experimental value (~6.5eV). When a Eu atom replaces one of the Sr atoms, Eu 4f majority-spin states appear in the forbidden gap of SrAl2O4, which is estimated to be 5.5eV above the valence band maximum. Considering spin–orbit coupling, Eu 4f majority-spin states decompose into two energy states and Eu 4f minority-spin states also appear in the band gap of SrAl2O4.