Becke-Johnson Potential Research Articles

Pressure effect on mechanical stability and optoelectronic behavior of Zinc-Silicon Diarsenide ZnSiAs2-Chalcopyrite: DFT investigation

The effect of hydrostatic pressure on the mechanical stability and optoelectronic behavior of zinc silicon diarsenide (ZnSiAs2) chalcopyrite were investigated by FP-(L)APW+lo method in the framework of the density functional theory (DFT). The exchange-correlation functional GGA-PBEsol was used for the prediction of structural and electronic properties. It was used also with the modified Becke-Johnson potential “TB-mBJ” for the prediction of the optoelectronic properties of ZnSiAs2. The values of the structural parameters, in particular lattice parameters, bulk modulus and its pressure derivative are close to the found values. The study of mechanical stability by the elastic model through generalized stability criteria confirms that ZnSiAs2 is stable mechanically under a pressure less than 10GPa. The elastic anisotropy of Young's modulus along (100), (110) and (111) planes was also studied. Band-gap calculated by TB-mBJ is very close to the experimental found values, which highlights the success of the TB-mBJ potential in the prediction of electronic properties. The calculation of the refractive index as well as the birefringence of the ZnSiAs2 by the use of GGA-PBEsol and TB-mBJ resulted in values close to those found experimentally and theoretically.

Electronic, optical, and thermoelectric properties of Fe2+xV1−xAl

We report the electronic, optical, and thermoelectric properties of full-Heusler alloy Fe2VAl with Fe antisite doping (Fe2+xV1−xAl) as obtained from the first-principles Tran-Blaha modified Becke-Johnson potential. The results are discussed in relation to the available experimental data and show good agreements for the band gap, magnetic moment, and optical spectra. Exploring our transport data for thermoelectric applicability suggest that Fe2+xV1−xAl is a good candidate with a high figure of merit (ZT) 0.75(0.65) for x = 0.25(0.50) at room temperature.

Electronic and Optical Properties of γ- and -Alumina by First Principle Calculations

The electronic and optical parameters of {\gamma}-Al2O3 and {\theta}-Al2O3 have been studied by using the first principle within the framework of density function theory (DFT). The computational approach is based on full-potential linearized augmented plane wave method (FP-LAPW) within the generalized gradient approximation (GGA), local density approximation (LDA), and modified Becke-Johnson potential (mBJ). The results show that these compounds have a direct gap ({\Gamma}-{\Gamma}) of about 5.375 eV and 4.716 eV for {\gamma}-Al2O3 and {\theta}-Al2O3, respectively. Several optical parameters of these materials are also investigated. The values of the real part of dielectric constant are found to be 3.259 and 3.694 for {\gamma}-Al2O3 and {\theta}-Al2O3, respectively, which are close to the experimental one (3.416). The refractive index is 1.806 and 1.922 for {\gamma}-Al2O3 and {\theta}-Al2O3 respectively, and shows a good agreement with the experimental result which is 1.86. GGA findings are consistent with the experimental results and are better than the other approximations. There are no salient differences between GGA and LDA results. The results advocate using this material as a transparent conducting layer in solar cell structure, which can be operated in a wide energy range.

Structural, Elastic, Electronic and Optical Properties of LaOAgS-Type Silver Fluoride Chalcogenides: First-Principles Study

First-principles density functional calculations were performed to investigate the structural parameters, elastic moduli and related properties, electronic band structure and optical properties of three LaOAgS-type barium silver fluoride chalcogenides BaAgChF (Ch denotes the chalcogenides S, Se and Te). The calculated structural parameters are in good accordance with the existing experimental data. The single-crystal and polycrystal elastic moduli were determined via the strain–stress technique. The investigated compounds show a strong anisotropic behaviour of the structural and elastic parameters. The calculated electronic band structure using the Tran–Blaha modified Becke–Johnson potential reveals that the three considered systems are large direct band gap semiconductors. The assignments of the energy band electronic states and chemical bonding character were accomplished with the help of the l-decomposed atomic densities of states diagrams. Frequency-dependent polarized optical functions were computed for an energy range from 0 eV to 30 eV. The microscopic origin of the electronic states that is responsible for the optical spectra structures were determined. The optical spectra exhibit a considerable anisotropy. Several trends in the variation of the considered physical properties with the atomic number Z of the chalcogenide Ch element in the BaAgChF series are observed.

Boron doped GaN and InN: Potential candidates for spintronics

The full potential linearized augmented plane wave method together with the Tran-Blaha modified Becke-Johnson potential is utilized to investigate the electronic structures and magnetism for boron doped GaN and InN. Calculations show the boron substituting nitrogen (BN defects) could induce the GaN and InN to be half-metallic ferromagnets. The magnetic moments mainly come from the BN defects, and each BN defect would produce the 2.00 μB total magnetic moment. The electronic structures indicate the carriers-mediated double exchange interaction plays a crucial role in forming the ferromagnetism. Positive chemical pair interactions imply the BN defects would form the homogeneous distribution in GaN and InN matrix. Moderate formation energies suggest that GaN and InN with BN defects could be fabricated experimentally.

Investigation of the structural, electronic and optical properties of the cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr and Ba) using modified Becke-Johnson exchange potential

The structural, electronic and optical properties of the cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba) have been investigated using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange and correlation potential was applied using the generalized gradient approximation for calculating the structural properties In addition, the modified Becke-Johnson (TB-mBJ) potential was used for calculating the electronic and optical properties. It was found that the lattice constant increases while the bulk modulus decreases with the change of cation (M) in going from Be to Ba in the RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba). The reflectivity and absorption properties were also studied using the mBJ method to understand the inter-band transitions and their possible applications in absorption devices in the UV-region.

Two haloid borate crystals with large nonlinear optical response.

The photophysical properties of the noncentrosymmetric haloid borates K3B6O10X (X = Cl or Br) are calculated using density functional theory within the recently modified Becke-Johnson potential. The calculated electronic band structure reveals that the theoretical direct band gaps, 5.21 eV (K3B6O10Cl) and 4.85 eV (K3B6O10Br), are in good agreement with the previous calculation for K3B6O10Cl (5.16 eV) and experimental data for K3B6O10Br (4.86 eV). The calculated absorption coefficients, refractive indices, and birefringence are also in good agreement with the experimental data. The calculated nonzero second harmonic generation (SHG) coefficients, d33, d22 (= -d21), and d15(= d32 = d31), show good agreement with the experimental values. Furthermore, we have obtained the microscopic first hyperpolarizability for the dominant tensor component of the SHG.

Electronic structures and half-metallicity of carbon doped bulk and surface CdS: The modified Becke-Johnson potential calculation

Abstract The electronic structures and ferromagnetism for bulk and surface CdS with CS defects are investigated by the full potential linearized augmented plane wave method together with the modified Becke-Johnson potential. Calculations show bulk and surface CdS with CS defects are half-metallic ferromagnet. Each CS defect could produce the total magnetic moment of 2.00 µB. Electronic structures indicate the stable ferromagnetism could be attributed to the p-d exchange-like p-p coupling mechanism. Sulfur vacancies would give rise to the magnetism vanishing. For the nonpolar ( 10 1 ¯ 0 ) surfaces, the CS defects prefer to occupy the surface layer sites.

Ab initio study of semi-classic transport coefficients of SnO2 thermoelectric material

Abstract54 The electronic structure and semi-classic transport coefficients of SnO 2 are investigated. The calculations are carried out by using the density functional theory and the Boltzmann transport equations. The exchange-correlation potential is treated by the Tran–Blaha modified Becke–Johnson potential (Tb-mBJ) approximation. The calculated band gap value of SnO 2 is found to be in good agreement with the experimental one. The thermoelectric properties reveal that the Seebeck coefficient, electrical conductivity and power factor are strongly dependent on the doping level and temperature. A doping approach is proposed to enhance the thermoelectric properties of SnO 2 . The factor of merit suggests that SnO 2 could be a good thermoelectric material.

Computational investigations on band structure and optical properties of the BeSexTe1-xalloys through the FP-LAPW approach

In this paper, we have theoretically explored the structural, electronic and optical properties of the zinc blende structure of ternary alloys using the full-potential linearized augmented plane wave (FP-LAPW) method within the density-functional theory (DFT) as implemented in the Wien2K code. The electronic properties were computed using the following two approximations: the generalized gradient approximation (GGA) and the Tran-Blaha-modified Becke-Johnson potential (TB-mBJ). The obtained results clearly show that ternary alloys exhibit large and direct band gaps while binary compounds are indirect band gap semiconductors.

Investigation of the electronic and optical properties of ZnS monolayer nanosheet: first principles calculations

In this paper, some of the electronic and optical properties of ZnS monolayer nanosheet have been calculated and compared with the bulk ZnS. The calculations were performed based on the density functional theory framework using full-potential linear augmented plane wave method, in which TB-modified Becke–Johnson potential has been considered for exchange–correlation term. The results show that the structural change of ZnS, from bulk to monolayer nanosheet, has dramatically affected its electronic and optical properties. The shift of van Hove singularities, variation of density of states, the appearance of energy gap in the valence band of ZnS monolayer nanosheet, and the elimination of degeneracy of the p and d orbitals in S and Zn atoms are some of the important effects. The calculated band gap of 3.88 eV, for bulk ZnS, is in good agreement with the experimental values. Also, there is a direct energy gap of about 3.22 eV for ZnS monolayer nanosheet. Compared to bulk ZnS, the optical anisotropy of ZnS monolayer nanosheet has significantly increased. With the structural change from the bulk ZnS to ZnS monolayer nanosheet, plasmon energies of ZnS monolayer are situated in the lower energies. We have proposed an equation for variations of refractive index as a function of wavelength and temperature, based on the experimental and ground-state data of bulk ZnS.

Approximations to the exact exchange potential: KLI versus semilocal

In the search for an accurate and computationally efficient approximation to the exact exchange potential of Kohn-Sham density functional theory, we recently compared various semilocal exchange potentials to the exact one [F. Tran et al., Phys. Rev. B 91, 165121 (2015)]. It was concluded that the Becke-Johnson (BJ) potential is a very good starting point, but requires the use of empirical parameters to obtain good agreement with the exact exchange potential. In this work, we extend the comparison by considering the Krieger-Li-Iafrate (KLI) approximation, which is a beyond-semilocal approximation. It is shown that overall the KLI- and BJ-based potentials are the most reliable approximations to the exact exchange potential, however, sizable differences, especially for the antiferromagnetic transition-metal oxides, can be obtained.

Manifestation of Anomalous Weak Space-Charge-Density Acentricity for a Tl4HgBr6 Single Crystal.

Density functional theory (DFT) calculations within the concept of the MBJ+U+SO (modified Becke-Johnson potential + U + spin orbit) approach were performed for a Tl4HgBr6 single crystal for the first time assuming weak noncentrosymmetry (space group P4nc). Excellent agreement was achieved between the calculated and experimental band-gap-energy magnitudes as well as the density of electronic states measured by the X-ray photoelectron spectroscopy method. It is a very principal result because usually the DFT calculations underestimate the energy-gap values. In the present study, we carry out calculations of the optical properties (absorption coefficient, real and imaginary parts of the dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient, and optical reflectivity dispersions). It has been established that the principal origin of the observed weak acentricity is determined by delocalized band states at the top of the valence band originating from the p states of the Br atoms.

Optical properties of titanium and iron doped 3C-SiC behaviors TB-mBJ

Using the formalism of the full potential linearized augmented plane wave (FP-LAPW) method with the Tran and Blaha modified Becke–Johnson potential (TB-mBJ), we investigated the electronic structure and optical properties of titanium and iron doped silicon carbide (3C-Si1-xTixC and 3C-Si1-xFexC, x= 0.0625 and 0.125). We found that the direct band gap of 3C-Si1-xTix C and 3C-Si1-xFex C increased with Ti and decreased with Fe. For the second study, we compared the optical properties for Ti doped 3C-SiC and Fe doped 3C-SiC. The optical conductivity of iron doped 3C-SiC is higher than Ti doped 3C-SiC. According to these results, the compound 3C-Si1-xFexC could be used to solar cell application. We suggest that Fe doped 3C-SiC could be used for solar cell application.

First-principles study on LaYbO3 as the localized f electrons containing system with MBJ–LDA + U approach

The electronic structure of LaYbO3 was investigated by the full potential linearized augmented plane wave plus local orbital (FLAPW+lo) method with the modified Becke–Johnson potential combined with the local density approximation correlation plus onsite Coulomb interaction (MBJ–LDA+U) for the sake of localized f electrons. This approach was suitable for evaluating electronic structure of LaYbO3 system from view point of calculation cost and time. The band gap, the difference in energy between the valence band (VB) and conduction band (CB), was estimated to be 6.0eVby the present method. The evaluated value was very close to the reported experimental value. In the VB, Yb 4f orbitals and O 2p orbitals were well hybridized each other to state predominantly. The lower potential region in CB was mainly composed of La 4f orbitals, while the upper region in CB was mainly consisted of La 5d orbitals.

First-principles calculation of structural, optoelectronic properties of the cubic AlxGayIn1-x-y N quaternary alloys matching on AlN substrate, within modified Becke–Johnson (mBJ) exchange potential

A theoretical study of zinc-blende quaternary alloys AlxGayIn1-x-y N (x=0.343, 0.468, 0.593 and y=0.375, 0.5, 0.625) grown on AlN substrate where the lattice match condition is 〈ABS−P〉y=1,25(1−x). The full-potential linearized augmented plane wave method (FP-LAPW) was used to determine the variations in the bandgap as well as the optical properties. The generalized gradient approximation of Wu and Cohen (WC-GGA) was employed for the exchange-correlation potential to calculate the structural properties and the modified Becke–Johnson potential (TB-mBJ) employed for greater generation of the band gap and the optical properties. The structural properties (lattice parameters and bulk modulus) were assessed for binary, ternary and quaternary compounds. Whenever possible, results were compared with experiments and calculations completed with other computational schemes. The theoretical study of the optoelectronic properties demonstrate that these materials are applicable for optical device working in UV spectrum.

Effect of Pressure on the Optical Properties of Cubic-BaF2 Scintillator Crystal: A First-Principles Investigation Using the Modified Becke–Johnson Potential

In this paper, the variation with hydrostatic pressure of some optical properties of the cubic-BaF2 scintillator crystal, including the dielectric function, the energy loss function, and the refractive index, has been studied. The calculations were performed using the full potential linear augmented plane waves (FP-LAPW) method based on density functional theory (DFT). The modified Becke–Johnson potential was selected for the exchange–correlation potential. It is shown that this potential can correctly predict the band gaps and optical properties of the BaF2 compound. The results show that the effect of pressure on the optical properties of BaF2 is quite remarkable in the energy range of 10–22 eV, while the static dielectric constant and static refractive index vary linearly with increasing the pressure. Our calculations show that the peaks in the imaginary part of the dielectric function shift toward higher energies with increasing the pressure and are mainly related to the electronic transitions from F-2p and Ba-5p orbitals to the conduction band. Furthermore, we show that the peaks of the energy loss function, particularly the plasmon frequency, shift to higher energies with increasing pressure.

Accurate prediction of band gaps and optical properties of HfO2

We report on optical properties of various polymorphs of hafnia predicted within the framework of density functional theory. The full potential linearised augmented plane wave method was employed together with the Tran–Blaha modified Becke–Johnson potential (TB-mBJ) for exchange and local density approximation for correlation. Unit cells of monoclinic, cubic and tetragonal crystalline, and a simulated annealing-based model of amorphous hafnia were fully relaxed with respect to internal positions and lattice parameters. Electronic structures and band gaps for monoclinic, cubic, tetragonal and amorphous hafnia were calculated using three different TB-mBJ parametrisations and the results were critically compared with the available experimental and theoretical reports. Conceptual differences between a straightforward comparison of experimental measurements to a calculated band gap on the one hand and to a whole electronic structure (density of electronic states) on the other hand, were pointed out, suggesting the latter should be used whenever possible. Finally, dielectric functions were calculated at two levels, using the random phase approximation without local field effects and with a more accurate Bethe–Salpether equation (BSE) to account for excitonic effects. We conclude that a satisfactory agreement with experimental data for HfO2 was obtained only in the latter case.

First principles study of structural, electronic, magnetic and elastic properties of Mg0.75TM0.25S (TM=Mn, Fe, Co, Ni)

The objective of this work is to predict the structural, electronic, magnetic and elastic properties of Mg1−xTMxS (TM=Mn, Fe, Co and Ni) compound in the zinc blende Ferromagnetic phase using first principal approach. The structural and elastic properties are performed using the generalized gradient approximation proposed by Wu and Cohen(WC-GGA). However, the electronic and magnetic properties have been performed using modified Becke-Johnson potential combined with the LDA correlation (mBJLDA). The results show that all compounds Mg1−xMnxS, Mg1−xFexS and Mg1−xNixS exhibit a half-metallic ferromagnetic character with 100% spin-polarization at the Fermi level, except Mg1−xCoxS is a metal. For each compounds study here, the total magnetic momentum is an integer equal to magnetic moments of TM atom in their free space charge value. Due to the p–d hybridization, there is a small local magnetic moment on the Mg and S sites; whereas, the local magnetic moments of TM atom reduce from their free space charge value. In addition, we investigate the mechanical behavior of MgS and Mg1−xTMxS; all compounds studied here are mechanically stable and exhibit a strong anisotropic behavior.

Half-metallicity and electronic structures for carbon-doped group III-nitrides: Calculated with a modified Becke-Johnson potential

The electronic structures and magnetism for carbon-doped group III-nitrides are investigated by utilizing the first principle method with the modified Becke-Johnson potential. Calculations show that carbon substituting cations (anions) would induce the group III-nitrides to be paramagnetic metals (half-metallic ferromagnets). Single carbon substituting nitrogen could produce 1.00μB magnetic moment. Electronic structures indicate that the carriers-mediated double-exchange interaction plays a crucial role in forming the ferromagnetism. Based on the mean-field theory, the Curie temperature for carbon-doped group III-nitrides would be above the room temperature. Negative chemical pair interactions imply that carbon dopants tend to form clustering distribution in group III-nitrides. The nitrogen vacancy would make the carbon-doped group III-nitrides lose the half-metallic ferromagnetism.