Becke-Johnson Potential Research Articles

Computational Prediction of Structural, Electronic, Elastic, and Thermoelectric Properties of FeVX (X = As, P) Half-Heusler Compounds

Structural, electronic, elastic, and transport properties of FeVX (X = As, P) half-Heusler (HH) compounds have been calculated using density functional theory (DFT). The generalized gradient approximation developed by Perdew–Burke–Ernzerhof (GGA-PBE) is utilized for the calculation of the structural properties and the mechanical parameters of FeVX (X = As, P), indicating that the studied compounds are mechanically stable. The Tran and Blaha-modified Becke–Johnson potential (TB-mBJ) is utilized to improve the investigation of the electronic structure and also indicates that the FeVX (X = As, P) compounds are narrow-gap semiconductors. Calculations of transport efficiency are performed using the semiclassical Boltzmann theory. The figure of merit ZT is near unity at room temperature, indicating that both compounds are good candidates for use in transport devices.

Theoretical study of the structural, energetic, electronic and magnetic properties of the host matrix LiGa5O8 doped with Cr3+

The persistent phosphorus LiGa5O8:Cr3+ has attracted considerable attention due to its application in biomedical images. In this work, we used ab initio calculations based on density functional theory to study the properties of this compound doped with Cr3+. Two types of calculations are considered: (1) Cr3+ impurity replacing the Ga3+ atom at the 8c site and (2) Cr3+ impurity replacing the Ga3+ atom at the 12d site. From these calculations, we determine the structural, electronic, energetic, and magnetic properties for LiGa5O8:Cr3+. The generalized gradient approximation GGA-PBEsol functional, and the modified Becke-Johnson potential were used to simulate the exchange and correlation effects. The result for the defect forming energy revealed that the Cr3+ impurity is preferred to occupy the 12d site of Ga3+. From the Bader analysis, it was possible to determine the dopant defect charge when inserted into the host matrix of LiGa5O8. Through the density of the state, it was determined that the valence electron configuration of the Cr3+ dopant is 4s0 3d3 (8c or 12d site). There is a magnetic moment in the unit cell of −3.0μB due to the presence of Cr3+ in the LiGa5O8 lattice.

Phase stability and optoelectronic characteristics of Ba1-xBexS: a DFT-based simulation.

The structural stability and optoelectronic properties of the ternary Ba1-xBexS alloys along with the pure binary compounds BaS and BeS in the rock-salt (B1) and zinc-blende (B3) phases were investigated by the density functional theory (DFT) within the full-potential linearized augmented plane wave (FP-LAPW) method implemented in the Wien2k package. The generalized gradient approximation of Wu and Cohen (WC-GGA) was used for the exchange-correlation potential (Vxc) to compute the equilibrium structural parameters, lattice constant (a), and bulk modulus (B). In addition to the GGA approach, the modified Becke-Johnson potential of Tran and Blaha (TB-mBJ) scheme coupled with the spin-orbit interaction was used to calculate the band gap energies. Results reveal that BaS, Ba0.75Be0.25S, and Ba0.5Be0.5S compounds are stable in the rock-salt phase, while Ba0.25Be0.75S and BeS are found to be stable in the zinc-blende phase. The computed results for the band structures and optical constants are compared with other available theoretical calculations and experimental measurements.

First-principles calculations of structural, electronic, and optical properties for Ni-doped Sb2S3

Antimony sulphide (Sb2S3) is a potential candidate for alternative material in solar cell application. The structural, electronic, and optical properties of Ni doped Sb2S3 were calculated using full potential linear augmented plane wave (FP-LAPW) based on popular density-functional theory (DFT). The equilibrium lattice parameters have been calculated using Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (PBE-GGA). The band structure and density of state for Ni-doped Sb2S3 have been determined using Tran Blaha modified Becke-Johnson (TB-mBJ) potential. Our results indicate that Ni doped Sb2S3 has lower band gap energy compare to pure-Sb2S3. The optical properties of Ni-doped Sb2S3 such as absorption coefficient, reflectivity, refractive index, energy-loss function and extinction coefficient are presented. The results demonstrate that Ni-doped Sb2S3 has higher optical absorption coefficient in the visible region than pure-Sb2S3 which is good for optoelectronic applications.

Anion replacement effect on the physical properties of metal halide double perovskites Cs2AgInX6 (X=F, Cl, Br, I)

This article is about structural, electronic, optical and thermoelectric properties of metal halide double perovskites Cs2AgInX6 (X = F, Cl, Br, I). These properties are computed using the highly accurate full potential linearized augmented plane wave method based of density functional theory. To acquire suitable ground state lattice parameters, generalized gradient approximation has been used. The calculated structural parameters are found in excellent agreement with the available literature. In addition, modified Becke-Johnson potential is taken into account for precise calculation of band structures. These structures discover the direct semiconducting nature of investigated compounds, however, value of the band gap decreases from F to I anion replacement. As consequences, the optical absorption edge shifts toward lower energies. To further evaluate physical behavior, thermoelectric properties such as Seebeck coefficients, thermal conductivities, electrical conductivities and figure of merits are also calculated. This study specifies present double perovskites as probable candidates for optical and thermoelectric devices.

Phonon phase stability, structural, mechanical, electronic, and thermoelectric properties of two new semiconducting quaternary Heusler alloys CoCuZrZ (Z = Ge and Sn)

For meeting the energy demand, the development of new and novel thermoelectric (TE) materials for power generation is very vital. In this draft, we have theoretically investigated two new quaternary CoCuZrZ (Z = Ge and Sn) Heusler alloys for their structural, mechanical, electronic, and TE properties. In the energy minimization process, the alloys are found to be non-magnetic in the ground state. Based on calculated phonon dispersion curves, formation energy, and elastic constants, we propose that both CoCuZrGe and CoCuZrSn are stable. Furthermore, the mechanical properties indicate that CoCuZrGe (CoCuZrSn) has a brittle (ductile) nature. The electronic properties examined in Perdew-Burke-Ernzerhof (PBE), PBEsol, and modified Becke-Johnson (mBJ) potential, all predict that reported systems are narrow-gap semiconductors (SCs). In addition, the temperature dependent TE properties have been studied by calculating the electronic thermal conductivity (κ), Seebeck coefficient (S), power factor (PF) and electrical conductivity (σ/τ). The obtained positive value of S conveys the materials as p-type SCs, with a maximum value of 26.2 μV/K for CoCuZrGe and 28 μV/K for CoCuZrSn. The σ/τ, κ, and PF show increasing trends with rising temperature. The PF is found to be 1.55 × 1012 WK−2m−1s−1 for CoCuZrGe and 1.38 × 1012 WK−2m−1s−1 for CoCuZrSn. The proposed semiconducting Heusler alloys may receive attention for a range of TE and spintronic applications.

Local Modified Becke-Johnson Exchange-Correlation Potential for Interfaces, Surfaces, and Two-Dimensional Materials

The modified Becke-Johnson meta-GGA potential of density functional theory has been shown to be the best exchange-correlation potential to determine band gaps of crystalline solids. However, it cannot be consistently used for the electronic structure of nonperiodic or nanostructured systems. We propose an extension of this potential that enables its use to study heterogeneous, finite, and low-dimensional systems. This is achieved by using a coordinate-dependent expression for the parameter c that weights the Becke-Russel exchange, in contrast to the original global formulation, where c is just a fitted number. Our potential takes advantage of the excellent description of band gaps provided by the modified Becke-Johnson potential and preserves its modest computational effort. Furthermore, it yields with one single calculation band diagrams and band offsets of heterostructures and surfaces. We exemplify the usefulness and efficiency of our local meta-GGA potential by testing it for a series of interfaces (Si/SiO2, AlAs/GaAs, AlP/GaP, and GaP/Si), a Si surface, and boron nitride monolayer.

Ferromagnetism, half-metallicity and spin-polarised electronic structures characterisation insights in Ca1−xTixO

ABSTRACTIn this study, we have computed the structural, electronic and half-metallic ferromagnetic properties of Ca1−xTixO compounds at concentrations x = 0.125, 0.25, 0.5 and 0.75 by employing the first-principle approaches of density functional theory. The generalised gradient approximation of Wu and Cohen (GGA-WC) is used to calculate the structural parameters, whereas the electronic structures and magnetic properties are characterised by the accurate Tran–Blaha-modified Becke–Johnson potential (TB-mBJ). The lattice constant, bulk modulus and indirect gap of CaO are in good agreement with other theoretical and experimental results. The Ca0.25Ti0.75O at x = 0.75 has metallic ferromagnetic nature. The Ca0.875Ti0.125O, Ca0.75Ti0.25O and Ca0.50Ti0.50O compounds have total magnetic moments of 2 μB per Ti atom with a half-metallic character, a spin polarisation of 100% and a large half-metallic gap of 1.345 eV for x = 0.125. Therefore, the Ca1−xTixO material with a low concentration of Ti is a true half-metallic ferromagnet and seems to be a promising candidate for semiconductor spintronics.

Study the optical properties of XC (X = Si, Ge and Sn) nanosheets using TB-mBJ exchange-correlation potential

In this work, dielectric function, energy loss function, absorption, refraction index and reflectivity of graphene-like nanosheets of Si-C, Ge-C and Sn-C are calculated in the presence of a polarized electric field parallel (E||x) and perpendicular (E||z) to the surface of the hexagonal nanosheets. Our calculations are based on the density functional theory (DFT) with full potential linearized augmented plane-waves (FP-LAPW) basis. Generalized gradient approximation (GGA) and the Tran & Blaha modified Becke-Johnson (TB-mBJ) potentials are used for exchange-correlation potential. The results show that the optical properties of all the nanosheets are extremely polarization-dependent and have a significant anisotropic behavior especially in the visible region of the electromagnetic waves. Furthermore, the calculated value of static dielectric constant by TB-mBJ is less than GGA and also it is increased as we go down the periodic table from Si to Sn in our nanosheets. Also, our findings by the two methods demonstrate that for the E||z polarization, the refraction index is nearly constant in the visible region for all the three nanosheets, which shows the promising applications of these nanosheets in optical fiber devices. Finally, since the band gaps obtained by TB-mBJ method are very close to the experimental band gap, the optical properties obtained by TB-mBJ potential of this work may be used for the future optoelectronic applications of these nanosheets.

Investigations of novel polymorphs of ZnO for optoelectronic applications

Being a promising candidate in next-generation optoelectronic applications, the study of new polymorphs of zinc oxide (ZnO) is receiving the great attention of researchers. In this article, we explore optoelectronic properties of seven polymorphs of ZnO such as wurtzite type, sphalerite type, germanium phosphide (GeP) type, 5-5 type, nickel arsenide (NiAs) type, β-beryllium oxide (BeO) type and cesium chloride (CsCl) type by using full-potential linearized augmented plane wave plus local orbital (FP-L(APW+lo)) method within Density Functional Theory (DFT). Tran-Blaha modified Becke-Johnson potential (TB-mBJ) along with Generalized Gradient Approximation (GGA) proposed by Perdew-Burke-Ernzerhof (PBE) as exchange-correlation has been used for the calculations of electronic and optical properties of seven polymorphs of ZnO. Our band structure calculations reveal the considered polymorphs of ZnO as wide bandgap semiconductors. The calculated band gap values of wurtzite type, sphalerite type, GeP type, 5-5 type, NiAs type, BeO type and CsCl type polymorphs of ZnO are 2.901 eV, 2.679 eV, 2.648 eV, 3.127 eV, 2.986 eV, 3.040 eV and 1.853 eV respectively. The wurtzite type, sphalerite type, 5-5 type, NiAs type, and BeO type polymorphs of ZnO exhibit direct bandgap while GeP type and CsCl type polymorphs show indirect bandgap. The optical spectra of these polymorphs of ZnO reveal different reflection, plasmon energies, optical absorption, and refractive indices are considerably anisotropic and present different values in the x- and z-direction. The z-component of the reflectivity and absorption spectra was found larger than the x-component in wurtzite type, 5-5 type and NiAs type polymorphs of ZnO, showing that large reflectivity and optical absorption along z-axis than the x-axis in these polymorphs. This study is believed to provide an interesting guideline for the low-cost and non-toxic new polymorphs of ZnO in cutting-edge optoelectronic applications.

Electronic and optical properties of gyrotropic α-Hg3S2Cl2: insights from an ab initio study

The optical spectra of gyrotropic α-Hg3S2Cl2 polymorph were calculated for the first time to give a deep insight into its band structure. The exchange–correlation potential was treated with the generalized gradient approximation and modified Becke–Johnson potential (MBJ) to improve the accuracy of electronic structure calculation. The detailed analysis of the low-energy electronic states near the Fermi level was conducted. The main contributions of the sulfur and chlorine p states are located at the top of the valence band, while the S/p and Hg/s states give main contribution to the bottom of the conduction band. The direct optical band gap of 3.19 eV is at the Г-points of Brillouin zone. The value of direct optical transitions, which was calculated by MBJ method, agrees very well with the experimental report on diffuse reflectance spectra. The reported structural and optical properties of α-Hg3S2Cl2 polymorph make it a potentially interesting compound for nonlinear optical applications.

Calculation of the structural, energetic, electronic, and magnetic properties of LiAl5O8 doped with Fe and Cr: Ab initio method

Ab initio calculations based on density functional theory are used to study the structural, energetic, electronic, and magnetic properties of lithium aluminate (LiAl5O8) spinel doped with Fe and Cr. Two possible schemes are considered: (1) doping with Fe or Cr at the Al3+ 8c site and (2) doping with Fe or Cr at the Al3+ 12d site. Exchange and correlation effects are described via the generalized gradient approximation PBEsol functional (structural properties) and the modified Becke-Johnson potential (defect formation energy, electronic structure, and magnetic properties). For each scheme, the local structure around the defect is predicted. Our calculations show that Fe and Cr prefer the octahedral site of Al. A Bader analysis shows that the defect charge is 3 + for both Fe and Cr. Calculation of the electronic structure shows that the 3d states of Cr3+ and Fe3+ are below the Fermi energy and within the band gap of LiAl5O8. For replacement of Al by Fe, the state density calculation shows that Fe3+ has a valence electron configuration of 4s03d5 (8c and 12d sites). For replacement of Al by Cr, it is found that Cr3+ has a valence electron configuration of 4s03d3 (8c and 12d sites). There is a magnetic moment in the unit cell due to the presence of Cr and Fe in the LiAl5O8 lattice.

Half-Metallic Ferromagnetism in Gd-Doped Ti1/2Mg1/2N Alloy: An ab initio Prediction

In this work, we have investigated the electronic and magnetic properties of gadolinium Gd-doped Ti0.5Mg0.5N alloy. The supercell of 32 atoms was generated by the Alloy Theoretic Automated Toolkit (ATAT), and then we have used first-principles calculations performed by the full-potential linearized augmented plane wave method based on the spin density functional theory within the generalized gradient approximation of Perdew-Burke-Ernzerhof and the modified Becke-Johnson potential. We have also performed GGA + U calculations describing the strong correlation between the 4f electrons in Gd. Both GGA and mBJ calculations have shown that Ti0.5Mg0.5N alloy depicted a semiconductor character with band gaps of 0.403 eV and 1.184 eV, respectively. The calculated atomic-resolved densities of states of Ti6Gd2Mg8N16 alloy predict the half-metallic character (HMs) with ferromagnetic order (FM) using the modified Becke-Johnson potential mBJ. We have also estimated the Curie temperatures by using the Heisenberg model in the mean field approximation.

Simulation within a DFT framework and experimental study of the valence-band electronic structure and optical properties of quaternary selenide Cu2HgSnSe4

We report data of simulation within a density functional theory (DFT) framework, employing different approaches for exchange correlation (XC) potential, of the electronic structure and experimental verification of these band-structure calculations using X-ray photoelectron spectroscopy (XPS) of Cu2HgSnSe4 crystal. The present studies indicate that fair good agreement of total density of states (DOS) with the valence band XPS spectrum of the Cu2HgSnSe4 crystal is derived when DFT simulation is performed within modified Becke-Johnson (mBJ) potential and taking into consideration Hubbard correction parameter U and spin-orbit (SO) coupling (mBJ–U–SO approach). The mBJ–U–SO calculation reveals the best fit of total DOS to the experimental valence band XPS spectrum as well as a fairly good energy gap value for this compound. The present theoretical data indicate that the principal contributors to the Cu2HgSnSe4 valence band are Se 4p states with their main input in upper and central portions of the band, while Sn 5 s and Hg 6 s states make prevailed contributions in its lower portion and the bottom is formed by Hg 5d states. The quaternary Cu2HgSnSe4 selenide is a direct gap semiconductor. Based on the present mBJ–U–SO band-structure data, the main optical constants are calculated indicating that the compound under consideration is a very promising optoelectronic material.

Half-metal calculations of CoZrGe half-Heusler compound by using generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ) methods

The structural and magnetic calculations of CoZrGe half-Heusler compound were investigated using generalized gradient approximation (GGA) and modified Becke-Johnson potential. First, the volume-energy curves were performed to determine which phase was more stable. According to that curve, the ferromagnetic (FM) phase was more energetically stable than non-magnetic (NM) phase. Then the total density of states and band structures were plotted using GGA and mBJ methods. Since the spin-up and spin-down electrons cut the Fermi energy level, they show metallic properties in the GGA method. Therefore, it is possible to say that CoZrGe half-Heusler compound is a metallic ferromagnetic material when GGA method is used. However, when the mBJ method was used, the band gap was seen around the Fermi energy level in spin up electrons. This showed that spin-up electrons had semiconductor properties and spin-down electrons had metallic nature. Thus, in the mBJ method, CoZrGe half-Heusler compound showed half-metal ferromagnetic nature. The Fermi energy level value in the GGA method was 0.586 Ry, while it was obtained as 0.601 Ry by using the mBJ method. This ensured that the Fermi energy level was higher when the mBJ method was used and the intersections in the GGA method was eliminated. Total magnetic moment is obtained as 1.00 μB/f.u. in both calculation methods. It has been clearly observed that these two different methods affected the Fermi energy level. Finally, CoZrGe half-Heusler compound can be used in spintronic calculations.

Electronic structures and magnetic behavior of Al-, Si-, P- and Cl-doped ZnS

Electronic and magnetic properties of ZnS doped with nonmagnetic elements Al, Si, P and Cl are calculated using density functional theory (DFT) with the generalized gradient approximation plus the modified Becke-Johnson potential (GGA+mBJ). The calculations reveal that Al-, Si- and P-doped ZnS exhibit half-metallic behavior with a total magnetic moment of 3.0, 2.0 and 1.0 μΒ respectively, while Cl-doped ZnS remains nonmagnetic. The spin-polarized electronic band structures calculations show that dopants induce impurity bands in ZnS band gap, reducing the gap value from 3.52 eV to 2.51, 2.83 and 3.35 eV for Al-, Si- and P-doped ZnS respectively. Besides, the defect formation energies calculations show that Al-, Si- and P-doped ZnS could be realized experimentally under the Zn-rich condition. Consequently, Al, Si and P could be promising nonmagnetic dopants to get ZnS-based diluted magnetic semiconductor (DMS).

Enhanced out-of-plane thermoelectric performance of Cmcm SnSe phase by uniaxial strain

The electronic structure and thermoelectric property of SnSe are calculated by first-principles methods and Boltzmann transport theory. The deformation potential approximation and single parabolic band model are employed to compute the relaxation time. Owing to the accurate electronic structure calculated by Tran-Blaha modified Becke-Johnson (TB-mBJ) potential, the theoretical data (Seebeck coefficient, electrical conductivity and figure of merit ZT) are in good agreement with experimental data. Results show that the uniaxial strain not only affects the electrical structure, but also changes the thermal conductivity. As the uniaxial strain increases, the band gap, density of states of mass (mdos) and inertia mass (mI) also increases, indicating that the Seebeck coefficient S increases, while the electrical conductivity σ decreases. At carrier concentration of 3×1018 cm−3, 4×1018 cm−3, 5×1018 cm−3, 6×1018 cm−3 and 7×1018 cm−3, the corresponding optimal value of ZT is 1.91, 2.78, 3.51, 4.17 and 4.73, respectively. These results show that the strain not only leads to a lower elastic property, which causes the phonon modes softening and phonon propagation slowing down, but also enhances the conduction band minimum (CBM) convergence, which improves the Seebeck coefficient. This work provides insightful data to understand the enhanced thermoelectric properties of SnSe induced by the strain.

Semilocal exchange-correlation potentials for solid-state calculations: Current status and future directions

Kohn-Sham (KS) density functional theory (DFT) is a very efficient method for calculating various properties of solids as, for instance, the total energy, the electron density, or the electronic band structure. The KS-DFT method leads to rather fast calculations; however, the accuracy depends crucially on the chosen approximation for the exchange and correlation (xc) functional Exc and/or potential vxc. Here, an overview of xc methods to calculate the electronic band structure is given, with the focus on the so-called semilocal methods that are the fastest in KS-DFT and allow to treat systems containing up to thousands of atoms. Among them, there is the modified Becke-Johnson potential that is widely used to calculate the fundamental bandgap of semiconductors and insulators. The accuracy for other properties like magnetic moment or electron density, that are also determined directly by vxc, is also discussed.

Ferromagnetic Half-Semiconductor (HSC) gaps in co-doped CdS: Ab-initio study

In this work we have used the density functional theory (DFT) to study structural, magnetic and electronic properties of Co doped CdS in the zinc-blende (ZB) phase. Three approximations have been used to treat the exchange-correlation potential: the (PBE) GGA, (PBE) GGA+U and the model of Tran–Blaha modified Becke–Johnson potential (TB-mBJ). The on–site Coulomb interaction correction given by the Hubbard U has been calculated by the local density approximation constraint for the Co electronic orbitals. The theoretical results show that all the properties under study are affected by the doping of Co atom. Co doped CdS becomes a Ferromagnetic Half-Semiconductors (HSC). The total magnetic moment increases with increasing Co concentration; reaching the value of 9 (in the units of Bohr magneton) at high concentration (x = 18.75 %). The total magnetic moment value is an integer in the GGA+U and TB-mBJ approximations. Furthermore, to validate the effects resulting from the exchange splitting process, we have calculated the values of the spin-exchange constants N0α and N0β, respectively. All these changes make CdS:Co extremely interesting system for the spintronic applications.

Comparison between optoelectronic spectra and NMR shielding in tellurium based compounds: a FP-LAPW study

The Nuclear Magnetic Resonance (NMR) of 125Te atom and optoelectronic spectra in the X2TeO3 (X = Na, K, Ag) and PbTeO3 compounds are investigated by the modified Becke-Johnson (mBJ) potential. Obtained magnetic shielding and the experimental chemical shifts are in close agreement. The X ions control polarity of the magnetic shielding around the 125Te nucleus and σiso(X) increases from Na2TeO3 to PbTeO3 compounds. Calculated band gap of X2TeO3 (X = Na, K, Ag) and PbTeO3 compounds are 3.23, 0.24, 3.63 and 3.95 eV, respectively. Density of states results show that the X1,2-p states in the bottom of the valence band have an essential role in the value of 125Te NMR chemical shielding. The magnetic shielding of X atoms governs on the optical properties, such as the static dielectric function, refractive indexes and plasmon energies.