Becke-Johnson Potential Research Articles

Optoelectronic Properties of Zinc Oxide: A First‐Principles Investigation Using the Tran–Blaha Modified Becke–Johnson Potential

In this work, density functional theory (DFT) is used to investigate the influence of semi‐local exchange and correlation effects on the electronic and optical properties of zinc oxide. It is found that the inclusion of such effects using the Tran–Blaha modified Becke–Johnson potential yields an excellent description of the electronic structure of this material giving an energy band gap which is systematically larger than the one obtained with standard local functionals such as the generalized gradient approximation. The discrepancy between the experimental and theoretical band gaps is then significantly reduced. We also calculated the dielectric functions of ZnO and find a violet shift to the absorption edge which is in good agreement with experimental results.

Electronic and optical properties of double perovskite oxide Pb2ScMO6 (M = Ta, Sb) using a first principles approach

In this study, the electronic and optical properties of the double perovskite (DP) oxides Pb2ScMO6 (M = Sb, Ta) were systematically investigated using the full-potential linearized augmented plane wave model. Calculations were performed using both the generalized gradient approximation and modified Becke–Johnson potentials. The results showed that the O-atom is responsible for the maxima in the density of states (DOS) in the valence band, whereas the Sc-atom contributes to the maximum DOS in the conduction band. The dielectric constants, absorption coefficients, and reflectivity were also calculated for these systems. The results indicated the presence of wide band gaps in both of these DPs, thereby indicating their insulating semiconducting nature.

Structural and electronic properties of VSb2 and FeSb2

Abstract This work was devoted to study of structural and electronic properties of compounds XSb2, where X can be iron (Fe) or vanadium (V). Thus, we have calculated the minimum total energy Emin, the compression modulus B (GPa), its derivative BP, the density of state “DOS” and band structure. We have been interested in this type of material because they are often used in electrochemical cells and photovoltaic solar cells .The calculations were performed by full-potential linearized augmented plane wave method (FP-LAPW) as part of the density-functional theory (DFT). To determine the exchange and correlation potential, we used the generalized gradient approximation “GGA” and the modified Becke-Johnson potential “mBJ” , which was recently published by Tran and Blaha. These methods are implemented in the code Wien2k.Subsequently; we calculated the electronic structure of the two materials, using GGA. The results obtained indicated that these compounds have a metallic character. This result has been confirmed by mBJ method for VSb2. Whereas for FeSb2, this last study showed a semiconductor character with a gap of 0.278 eV.

Electronic Structure for Europium Chalcogenides with Modified Becke–Johnson Potential Plus an On-Site Coulomb U (mBJ+U)

The full potential linearized-augmented-plane-wave (FP-LAPW) method is generalized to a case of an all-electron fully-relativistic spin-polarized self-consistent band calculation based on the relativistic spin-density functional theory and the modified Becke–Johnson potential (TB-mBJ) plus an on-site coulomb U employed for greater generation of the band gap. The results show that these materials are semiconducting materials. The indirect energy gap obtained in this calculation is 1.63[Formula: see text]eV, 1.79[Formula: see text]eV and 1.96[Formula: see text]eV for EuS, EuSe and EuTe, respectively. It is clear from the plots that LSDA[Formula: see text][Formula: see text][Formula: see text]U is a poor technique for the calculation of the band gaps of chalcogenides (EuX). The calculated results for EuX (S, Se and Te) by mBJ[Formula: see text][Formula: see text][Formula: see text]U are in good agreement with the experimental values as compared to the other calculated results.

Spin-polarized optical properties of half-metallic binary XBi (X = Ca, Sr and Ba) compounds in zinc blende and wurtzite phases

In this work, we aim to study the spin-polarized optical properties of the non-transition metal-based binary compounds XBi (X = Ba, Sr and Ca) in the zinc blende and wurtzite phases. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals (FP-L/APW + lo) method within the spin density functional theory. We used the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (PBE-GGA) and the recently modified Becke–Johnson potential (mBJ-GGA) to generate the exchange–correlation potential. The optical constants as the dielectric function, refractive index and extinction coefficient were calculated and discussed in detail. Our compounds are identified as potential candidates for spintronic applications and high-performance electronic devices, due to their possible half-metallic character. The interband transitions responsible for the structures in the spectra are specified. It is shown that the Bi-p states and (Ca, Sr, Ba)-d states play the major role in optical transitions as initial and final states.

Composition dependent tuning of electronic and magnetic properties in transition metal substituted Rock-salt MgO

Abstract Full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT) is used to investigate the structural, electronic and magnetic properties of Fe and Ni (3d transition metal) substituted Rock-salt wide band gap insulator M g 1 - x M x O (M = Fe, Ni). We have performed spin polarized calculations throughout this work with generalized gradient approximation (GGA) type exchange correlation functional. Additionally, the electronic structures and density of states are computed using modified Becke-Johnson (mBJ) potential based approximation with the inclusion of coulomb energy (U = 7 eV). Based on the Vegard’s law and structural optimization, the lattice parameter and bulk modulus are found to be in good agreement with experimental values. Moreover, the analysis of electronic band structures reveals an insulating character for Ni substituted MgO while semiconducting and half-metallic character for Fe substituted case. It has been found that the p-d super-exchange interaction provides a ferromagnetic character due to the 3d transition metal impurities and oxygen atom. The observed p-d hybridization at the top of the valence band edge in this investigations could be useful for magneto-optic and spintronic applications. PACS: 61.66.Dk; 71.15.Mb; 71.15.Nc; 71.20.Nr; 71.22.+ i.

Investigation of Electronic, Magnetic, Thermodynamic, and Thermoelectric Properties of Half-Metallic XLiSn (X = Ce, Nd) Alloys

We have investigated the electronic, magnetic, thermodynamic, and thermoelectric properties of half-Heusler CeLiSn and NdLiSn using density functional theory. The materials crystallize in $$ F\overline{4}3m $$ structure with ferromagnetic state at optimized lattice parameter of 6.73 A for CeLiSn and 6.74 A for NdLiSn. The modified Becke-Johnson potential (mBJ) and generalized gradient approximation (GGA) have been used for computation of band structure, where mBJ shows a perfect half-metallic nature of the bands in both the alloys. The calculated magnetic moment of 1.0 μB for CeLiSn and 3.0 μB for NdLiSn follow Slater-Pauling rule, with ferromagnetic interactions. The temperature variation of the Seebeck coefficient shows the p-type behavior with room temperature values of 27 μV/K (43 μV/K) for CeLiSn (NdLiSn). Pressure-dependent variation of specific heat, Debye temperature, and Gruneisen parameter were calculated to infer the nature of lattice vibration and stability at high pressures.

The anisotropic thermoelectricity property of AgBi3S5 by first-principles study

The electronic and thermoelectric properties of AgBi3S5 are calculated using the first-principles calculations with Boltzmann transport theory. Because of accurate electronic structure calculated by Tran-Blaha modified Becke-Johnson (TB-mBJ) potential, the theoretical data (Seebeck coefficient, electrical conductivity, power factor and zT) are in good agreement with experimental data. When the temperature increases from 300 K to 800 K, the optimal peak value of zT along x axis, y axis and z axis changes from 0.17 to 1.22, from 0.42 to 2.24 and from 0.18 to 1.05, respectively. Our calculations suggest that the largest zT value obtained along y axis is 2.24 at T = 800 K and n = 5.73 × 1019cm−3. These results give a valuable theoretical guidance for the high-performance thermoelectric materials through anisotropic performance.

Insight into the structural, elastic and electronic properties of tetragonal inter-alkali metal chalcogenides CsNaX (X=S, Se, and Te) from first-principles calculations

To investigate the structural, elastic and electronic properties of the tetragonal inter-alkali metal chalcogenides CsNaX (X = S, Se, and Te), we have applied the full-potential linearized augmented plane-wave plus local orbital (FP-LAPW + lo) method within the density functional theory (DFT) framework. For the description of the exchange-correlation potential, the Wu-Cohen generalized gradient approximation (WC-GGA) was employed. Furthermore, the generalized gradient approximation of Engel and Vosko (EV-GGA) and Tran-Blaha modified Becke-Johnson (TB-mBJ) potential were also applied to obtain reliable results for the electronic properties of CsNaX compounds. Our optimized equilibrium structural parameters are in good agreement with experimental measurements where available. The Young's modulus, bulk modulus, shear modulus, Poisson's ratio, Pugh's ratio, acoustic velocities and Debye temperature were derived from our estimated elastic constants Cij. It is found that all the considered compounds are mechanically stable and ductile in nature. In addition, the elastic anisotropy of the examined compounds was studied by visualizing the directionally dependent Young's modulus, shear modulus and compressibility, as well as by calculating some elastic anisotropy indices. Electronic properties, such as the band structure, density of states and the charge density, were analyzed in detail. Calculated band structures show that the studied materials are semiconductors with indirect band gaps (Z-Γ).

Exploring Exemplary Optoelectronic and Charge Transport Properties of KCuX(X=Se,Te)

We report the electronic structure, optical and charge transport properties of the unexplored ternary Zintl phases KCuX(X=Se,Te) from the first principles calculations employing the full-potential linearized augmented plane-wave (FLAPW) method with the Tran Blaha modified Becke-Johnson (TBmBJ) potential. It is demonstrated that the materials are direct band gap (1.13, 1.38 eV) semiconductors with covalent bonding between Cu and (Se/Te). The calculated low effective mass and high carrier mobility (over 105 cm2/V.s) accentuate that KCuX have good carrier transport and the materials may have possible applications in solar cell absorbers and nanoelectronic devices. Absorption spectra indicates that the ternary crystals are UV-A light absorbers and could be useful in photovoltaic and photodetector applications. A study on the effect of pressure (till 5 GPa) is carried out in order to further explore the materials for their electronic band gaps and charge transport properties as they are proposed to be useful in future contemporary electronic devices. It is observed that pressure enhances the intrinsic carrier mobility and thermal stability of KCuX, indicating that the materials can withstand robust external conditions.

Investigations of half-metallic ferromagnetism and thermoelectric properties of cubic XCrO3 (X = Ca,Sr,Ba) compounds via first-principles approaches

In this paper, the physical aspects of the cubic phase XCrO3 (X=Ca,Sr,Ba) perovskites are studied by employing full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. These compounds have been found stable in ferromagnetic (FM) phase since they possess lower energy in FM phase compared to non-FM phase and their stability is also confirmed by calculating the enthalpy of formation (ΔH). The electronic structures of these compounds are analyzed with Trans and Blaha modified Becke–Johnson potential (TB-mBJ) for both spin up and spin down channels, which indicate their half-metallic characters. Analysis of density of states (DOS) shows major contributions of O-2p states in the valence band and Cr 3d-state in conduction band. A comparative analysis of crystal field effect (ΔEcrystal) and the exchange energies (direct Δx(d) and indirect Δx(pd)) tells about the main part of electronic spin in ferromagnetic character. The calculated magnetic moments make these compounds favorable for spintronic applications. In the end, thermoelectric parameters are computed for 200 K–800 K temperature range to explore potential of these compounds for applications in renewable energy devices.

Electronic band-structure and optical constants of Pb2GeS4: Ab initio calculations and X-ray spectroscopy experiments

The electronic band-structure of the ternary sulfide Pb2GeS4 was investigated by combining experimental and theoretical methods. Binding energy (BE) values of core electrons of Pb2GeS4 are measured employing X-ray photoelectron spectroscopy (XPS) for as-synthesized and treated with Ar+-ions crystal surfaces. The XPS measurements indicate that Ar+-ion treatment does not change the BE values of the core-level electrons of atoms constituting the Pb2GeS4 single crystal as well as peculiarities of the XPS valence band (VB) spectrum. The treatment does not cause changes in the crystal surface stoichiometry. The band-structure calculations based on density functional theory (DFT) reveal total density of states and partial densities of states of Pb2GeS4 within different exchange–correlation approximations. The best fit with the experiment is derived when the DFT calculations of Pb2GeS4 employ modified Becke-Johnson potential with Hubbard-corrected functional and taking into account spin–orbit (SO) interaction. The calculations indicate that top and upper portion of the VB is composed mainly by S 3p states, its central portion is formed by Ge 4p and S 3p states, while contributions of Pb 6s states dominate at its bottom with slightly smaller contributions of Ge 4s states as well. Contributions of unoccupied Pb 6p states dominate at the conduction band (CB) bottom. Regarding the occupation of the VB by Ge 4p and S 3p states, the theoretical data are confirmed experimentally by matching the XPS VB spectrum on a common energy scale with the X-ray emission spectra representing the valence S p and Ge p states. The present calculations yield that the VB maximum is positioned at the Y point, while the CB minimum at the Г point; this fact indicates that Pb2GeS4 sulfide is an indirect-gap material. The principal optical constants are also elucidated using the ab initio DFT calculations.

Half-Metallic Ferrimagnetism in CoFeNbZ (Z = Al, Si, Ge, Sn) Quaternary Heusler Alloys: a DFT Study

First principles calculations based on density functional theory is used to study the structural, electronic, and magnetic properties of novel CoFeNbZ (Z = Al, Si, Ge, Sn) quaternary Heusler alloys with the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation effects are treated using generalized gradient approximation (GGA) to study the structural properties. With GGA as the exchange-correlation potential, CoFeNbAl and CoFeNbSn are half-metallic with 100% spin polarization, whereas CoFeNbSi and CoFeNbGe are nearly half-metallic with high spin polarization of 90.06 and 98.28% respectively. For CoFeNbAl and CoFeNbSn, the spin-flip gap increases with the use of modified Becke-Johnson potential. Using this approximation, CoFeNbGe is a half-metal with a spin-flip gap of 0.303 eV. The magnetic properties indicate that all the compounds follow the Mt = Zt - 24 Slater-Pauling rule. The half-metallic behavior is maintained over a relatively wide range of lattice constants against hydrostatic strain. The transport properties of half-metallic CoFeNbZ (Z = Al, Ge, Sn) compounds are reported. Our present work has the potential to trigger the design of quaternary Heusler alloys with applications in spintronic devices.

Structural, electronic and optical properties for chalcopyrite semiconducting materials: ab-initio computational study

Investigation of the physical properties of chalcopyrite materials using ab-initio methods have been carried out to simulate a new structure of thin-films photovoltaic cells with high conversion efficiency. The Density Functional Theory calculations have been performed using Wien2k computational package by employing the full-potential linearized augmented plane wave method. Structural and electronic properties of chalcopyrite semiconducting material Copper–Indium–Gallium–Selenium i.e. CuIn1-xGaxSe2 have been investigated using local density approximation for the exchange-correlation potential. The electronic structures and linear optical properties have been studied using both the semi-local Becke-Johnson potential and its modified form i.e. mBJ and TB-mBJ. Computational results are in good agreement with those acquired experimentally. The viability of alloys in realization of ultra-thin-film based (CIGS) solar cells with high performance has been proposed after simulation and analysis study using one of solar cell simulation tools. The studied material exhibits capability to become a promising candidate for fabrication of optoelectronic and photovoltaic devices.

Electronic and Transport Properties of LaNi4Sb12 Skutterudite: Modified Becke–Johnson Approach

We carried out an ab␣initio study of structural, electronic, thermodynamic, and thermoelectric properties of the lanthanum-filled skutterudite, LaNi4Sb12. Generalized gradient approximation and modified Becke–Johnson potentials were employed for the exchange–correlation potential. The electronic structure calculations display the metallic behavior of the compound. The alloy offers low lattice thermal conductivity along with a high Seebeck coefficient with a value of − 158 (μVK−1) at room temperature. The effect of high pressure and temperature on thermal properties like thermal expansion coefficient, heat capacity, and Gruneisen parameter are also investigated by means of a quasi-harmonic Debye model. The large Seebeck coefficient and high power factor exhibited by LaNi4Sb12 make it an attractive candidate for thermoelectric materials.

Electronic, optical and thermoelectric investigations of Zintl phase AE3AlAs3 (AE = Sr, Ba): First-principles calculations

First principles calculations were performed to investigate the electronic, optical and thermoelectric properties of Zintl orthorhombic phase AE3AlAs3 (AE = Sr, Ba) compounds using the full potential linearized augmented plane wave method. The exchange-correlation potential is treated with the generalized gradient approximation (GGA) and modified Becke-Johnson potential (TB-mBJ) to improve the electronic structure calculations. These two compounds are semiconductors have direct band gaps. The optical transitions are investigated via dielectric function along with other related optical constants such as refractive index and absorption coefficient. Thermoelectric properties are examined using the combination of electronic structure and Boltzmann transport theory. In detail, the calculated results of Seebeck coefficient, electrical and thermal conductivity, figure of merit and power factor are reported as a function of temperature.

Ab-initio study of electronic, magnetic and thermoelectric behaviors of LiV2O4 and LiCr2O4 using modified Becke-Johson (mBJ) potential

Owing to the large energy storage capacity and higher working voltage, the spinel oxides LiV2O4 and LiCr2O4, have remained under intense research attention for utilization as electrode materials in lithium-ion batteries. In this study, we explore the half-metallic nature and thermoelectric response in both LiV2O4 and LiCr2O4 spinel oxides using ab-initio density functional theory (DFT) based computations. The ground-state energies of these compounds have been studied at the optimized structural parameters in the ferromagnetic phase. In order to obtain a correct picture of the electronic structure and magnetic properties, the modified Becke-Johnson (mBJ) potential is applied to compute the electronic structures. The half-metallic behavior is confirmed by the spin-polarized electronic band structures and density of state plots. The magnetic nature is elucidated by computing the John-Teller energy, direct and indirect exchange and crystal field splitting energies. Our computations indicate strong hybridization decreasing the V/Cr site magnetic moments and increasing magnetic momenta at the nonmagnetic atomic sites. We also present the computed parameters significant for expressing the thermoelectric response, which are electrical conductivity, thermal conductivity, See-beck coefficient and power factor. The computed properties are of immense interest owing to the potential spintronics and Li-ion battery applications of the studied spinel materials.

Effect of pressure on structural, electronic and optical properties of SrF2: a first principles study

We report results of the first principles calculations of structural, electronic and optical properties of SrF2 under pressure, performed using full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory as implemented on WIEN2k code. The exchange-correlation energy functional has been treated with generalised gradient approximation (GGA) for structural optimization,while the Tran-Blaha modifed Becke-Johnson potential (TB-mBJ) has been employed for electronic and optical calculations. Our results show that the first transition from Fm3m to Pnam structure occurs at 5.8 GPa and the second transformation from Pnam to P63/mmc structure takes place at 24.8 GPa. Our electronic calculation indicates an indirect gap X-Γ of Fm3m structure, direct gap Γ-Γ of Pnam structure and indirect gap Γ-K of P63/mmc structure. We do not observe the metallization up to 210 GPa. The linear optical properties such as absorption coefficient, reflectivity, refraction index, conductivity and energy loss function have been derived from calculated complex dielectric function for a wide energy range of 0-50 eV and pressure up to 50 GPa, and analyzed in detail.

Effect of Varying Pnictogen Elements (Pn=N, P, As, Sb, Bi) on the Optoelectronic Properties of SrZn2Pn2

Abstract Pnictogen-based Zintl compounds have fascinating properties. Nowadays these compounds have gained exceptional interest in thermoelectric and optoelectronic fields. Therefore, in this work the structural, electronic and optical properties of SrZn2Pn2 (Pn=N, P, As, Sb, Bi) compounds were studied using state-of-the-art density functional theory. The optimised lattice parameters (ɑ, c, c/ɑ and bond lengths) are consistent with the experimental results. The bulk moduli and c/a showed a decrease when changing the Pnictogen (Pn) anion from N to Bi in SrZn2Pn2 (Pn=N, P, As, Sb, Bi). The modified Becke-Johnson potential is used for band structure calculations. All compounds show semiconducting behaviour except SrZn2Bi2, which is metallic. Pn-p, Zn-d and Sr-d play an important role in defining the electronic structure of the compounds. The optical conductivity and absorption coefficient strength are high in visible and ultraviolet regions. These band structures and optical properties clearly show that SrZn2Pn2 compounds are potential candidates in the fields of optoelectronic and photonic devices.

Structural, electronic and thermoelectric properties of the intermetallic materials based on Mg2X (X= Si, Ge, Sn): DFT calculations

The scope of this work is the investigation of the physical properties of chalcopyrite materials using ab-initio methods in order to simulate a new structure of thin-films photovoltaic cells with high conversion efficiency. In the first framework, we obtained the results of calculations based on Density Functional Theory (DFT) using the full-potential linearized augmented plane wave method (FP-LAPW) as involved in the WIEN2K computational package. For the exchange-correlation potential, the local density approximation (LDA) was used to calculate the lattice parameters, Bulk modulus and its first derivative as well as the densities of states of the intermetallic semiconductors materials based on Mg2X (X=Si, Ge and Sn). The semi-local Becke-Johnson (mBJ) potential and its modified form proposed by Tran and Blaha (TB-mBJ) were also used for studying the electronic and thermoelectric properties; (merit factor, Seebeck coefficient, electronic conductivity). The achieved results were compared to computational works and other data acquired experimentally.