Modified Becke-Johnson Research Articles

First-principles calculations to investigate structural, electronic, mechanical and optical properties of SrAlO3 compound

In this study, density functional theory calculations were used to investigate the structural, electronic, mechanical, and optical properties of SrAlO3 perovskites. Calculations were performed using WEIN2K with the Generalized Gradient Approximation (GGA) and modified Becke-Johnson (MBJ) methods. The present compound shows large band gap around 5.67 eV for GGA method and 6.70 eV for MBJ method. The band structure (BS) and partial density of states (PDOS) reveal the predominant involvement of the oxygen-p orbital in the valence band, while the Al and Sr-s, p and d orbital contribute significantly to the conduction band, that play a significant role in determining the electronic and optical properties. Using the GGA and MBJ methods, the optical properties of SrAlO3 have been determined in terms of optical conductivity, dielectric constant, absorption coefficient, energy loss, optical reflectivity, and refractive index. It has been noted that the features present in the optical absorption spectra obtained experimentally match those of the simulated spectra featuring an oxygen vacancy. We use elastic constants to describe a material's mechanical properties. Under normal conditions, these materials' elastic constants demonstrate their mechanical stability. We meticulously determined the elastic constants by graphing the directional variations of compressibility, Young's modulus, and shear modulus. Our findings indicate that these chemicals have high elastic constants. Furthermore, we collect and interpret the phonon spectra. Complete phonon dispersion simulations validate the dynamic stability of the SrAlO3.

Bandgap of two-dimensional materials: Thorough assessment of modern exchange-correlation functionals.

The density-functional theory (DFT) approximations that are the most accurate for the calculation of bandgap of bulk materials are hybrid functionals, such as HSE06, the modified Becke-Johnson (MBJ) potential, and the GLLB-SC potential. More recently, generalized gradient approximations (GGAs), such as HLE16, or meta-GGAs, such as (m)TASK, have also proven to be quite accurate for the bandgap. Here, the focus is on two-dimensional (2D) materials and the goal is to provide a broad overview of the performance of DFT functionals by considering a large test set of 298 2D systems. The present work is an extension of our recent studies [T. Rauch, M. A. L. Marques, and S. Botti, Phys. Rev. B 101, 245163 (2020); Patra et al., J. Phys. Chem. C 125, 11206 (2021)]. Due to the lack of experimental results for the bandgap of 2D systems, G0W0 results were taken as reference. It is shown that the GLLB-SC potential and mTASK functional provide the bandgaps that are the closest to G0W0. Following closely, the local MBJ potential has a pretty good accuracy that is similar to the accuracy of the more expensive hybrid functional HSE06.

Ab initio thermochemistry study of polymorphism in the Si2N2(NH) analog of Si2N2O

We present a systematic density functional theory (DFT) study of the structural, bonding and electronic properties of the Si2N2(NH) polymorphs. This recently synthesized compound is a direct analog of Si2N2O in which the oxygen is replaced by an NH group. We show that a local-density approximation (LDA) description in the static lattice approximation gives a good account of the lowest energy orthorhombic phase of both the parent oxide and imide analog. In this work we extend our systematic comparisons between Si2N2O and Si2N2(NH) to denser tetragonal and monoclinic polymorphs. For Si2N2(NH) we find that the tetragonal and monoclinic polymorphs have energies 0.8 and 1.8 eV higher than (respectively) that of the orthorhombic ground state, similar to their Si2N2O counterparts (0.6 and 1.4 eV, respectively). We elucidate differences in chemical binding in Si2N2O and Si2N2(NH) polymorphs using Bader charge analysis and conclude that the imide systems possess slightly less ionic character than their oxide counterpart. Using the modified Becke-Johnson (MBJ) meta-LDA approach we find that orthorhombic Si2N2O and Si2N2NH have direct gaps of 5.65 and 5.75 eV, respectively, in excellent agreement with experiment. Relative to the orthorhombic Si2N2O (5.65 eV, direct), the band gaps in the denser polymorphs increase and become indirect (tetragonal: 5.72 eV, monoclinic: 6.06 eV). We find more complex trends in Si2N2NH in which the band gaps are also indirect in character, but decrease to 3.91 eV in the tetragonal phase, and then increase to 4.18 eV (Γ → D) in the monoclinic case.

Defect levels from SCAN and MBJ meta-GGA exchange-correlation potentials

For more than a decade the HSE06 hybrid exchange-correlation functional developed by Heyd, Scuseria and Ernzerhof has provided a tool for reliable defect level calculations in density functional theory for which postprocessing tools are not necessary, in contrast to previous calculations using semilocal density functionals. One of the main reasons for its reliability is the high precision of HSE06 for band gap calculations. Recently, other functionals from the meta-generalized gradient approximation (meta-GGA) class have been used extensively to calculate the electronic properties of solids. In particular, band gaps can be accurately evaluated with the modified Becke-Johnson (MBJ) potential, and relaxed atomic structures close to experimental findings can be obtained with the strongly constrained and appropriately normed (SCAN) exchange-correlation functional. Both approaches are computationally cheaper than HSE06, and we consider here their performance for defect level calculations. We compare results for the $\ensuremath{\epsilon}(+/0)$ transition levels of seven donors and $\ensuremath{\epsilon}(0/\ensuremath{-})$ transition levels of four acceptors in group IV semiconductors. We conclude that in certain situations where HSE06 cannot be applied because of excessive computational costs, SCAN and MBJ might provide a good alternative.

Investigation of the Structural and the Electronic Properties of AgGaX2(X = S, Se, Te) Nanolayers in the [112] Direction by using Density Functional Theory

The structural and electronic properties of AgGaX2(X = S, Se, Te) nanolayers were studied by using a full potential linear augmented plane wave (FP-LAPW) based on density functional theory. To investigate the structural and electronic properties of nanolayers, the generalized gradient approximation of Perdew, Becke and Ernzerhof (GGA-PBE) and modified Becke-Johnson (MBJ) exchange potential were used, respectively. The studied nanolayers were confined in an orthorombic supercell and simulated in the [112] direction, and the effects of dangling bonds and the nanolayer thickness on the electronic and structural properties were explored. Also, the cohesive energy was calculated to investigate the nanolayers stability of AgGaX2(X = S, Se, Te) and the total and the partial densities of states were plotted to consider the electronic properties. The nanolayers were semiconductors, which is in good agreement with the experimental results. Moreover, the effects of surface and center atoms on the electronic properties were considered, as were the effects of dangling bonds and nanolayer thickness on the band gap energy.

Calculations within DFT framework of the electronic and optical properties of quaternary sulfide Tl2PbSiS4, a prospective optoelectronic semiconductor

We report results of computation within framework of density functional theory (DFT) of the electronic band-structure of quaternary thallium lead silicon sulfide, Tl2PbSiS4. Especially, we employ different approaches for exchange correlation (XC) potential to find the best fit of the theoretical total density of states (TDOS) curve to the experimental valence band (VB) spectrum as elucidated employing the method of X-ray photoelectron spectroscopy (XPS). The present findings indicate that the best fit of the experimental and theoretical data regarding the shape of the VB XPS spectrum and TDOS is derived when employing in the computation procedure for XC potential the modified Becke-Johnson (MBJ) approach, which includes also spin-orbit (SO) effect and Hubbard parameter U for strongly correlated electrons of d symmetry (MBJ + U + SO technique). Based on these findings, we have performed computation of the electronic band-structure and primary optical constants of Tl2PbSiS4. The MBJ + U + SO calculations present that the main contributors at the top of the VB in this quaternary sulfide are S 3p states, the central portion is prevailed by the input of S 3p and Si 3p states, while the bottom is determined by contributions of the electronic states of s symmetry associated with lead and silicon.

Infrared spectroscopy on electronic structures of platinum-group metal pernitrides MN2 (M = Ru, Rh, Ir, and Pt)

The electronic structures of platinum-group metal pernitrides MN2 (M = Ru, Rh, Ir, and Pt) were investigated via synchrotron radiation infrared spectroscopy and first-principles calculations. Measured reflectance spectra of marcasite-type RuN2 and RhN2 showed Drude-like responses, approaching 1 as the photon energy was decreased, whereas reflectance of arsenopyrite-type IrN2 and pyrite-type PtN2 became ∼0.3 in the low photon energy region with a few features. These findings agreed well with the predictions of the metallic nature of marcasite-type RuN2 and RhN2 and the semiconducting properties of arsenopyrite-type IrN2 and pyrite-type PtN2, respectively. The measured reflectance spectra were also reasonably consistent with the calculated optical responses. The band gaps of IrN2 and PtN2 were estimated to be 0.8 and 2.1 eV, respectively, via first-principles calculation with a modified Becke–Johnson (MBJ) potential for the exchange potential.

Electronic band structure and basic optical constants of TlGaSn2Se6, a promising NLO semiconductor: First-principles calculations under DFT framework

We present results of band-structure computation under framework of density functional theory (DFT) of total and partial densities of states (DOS) of quaternary thallium gallium tin selenide, TlGaSn2Se6, a novel and promising material for application in non-linear optics. The present computation data are obtained employing different approaches for exchange-correlation (XC) potential to uncover the best fit of theoretical DOS curves to the experimental valence band (VB) spectrum of TlGaSn2Se6 compound as measured by X-ray photoelectron spectroscopy. Our findings show that the best fit of the theoretical and experimental data are detected in the case of application for XC potential of modified Becke-Johnson (MBJ) approach and involving in the computation procedure of the spin-orbit (SO) effect and the correction parameter U for highly correlated electrons of d symmetry. Based on our findings, we calculate band structure and primary optical constants of the quaternary thallium gallium tin selenide. The calculations indicate that this selenide is an indirect gap semiconductor in which the main input at the top und upper constituent of the TlGaSn2Se6 VB comes from Se 4p states, its central part is dominated by contributions of Sn 5p states. Further, Tl 6 s and Ga 4 s states are the most substantial contributors to the lower VB portion, while the VB bottom is prevailed by contributions of Sn 5 s states.

Theoretical investigation of lattice dynamics, dielectric properties, infrared reflectivity and Raman intensity spectra of Nowotny chimney-ladder semiconducting silicide Ru2Si3

Abstract Semiconducting silicides are highly promising materials for applications in thermoelectric, photovoltaic and optoelectronic devices. Here, using ab-initio density functional theory, the lattice dynamics, dielectric properties, Infrared (IR) refletivity and Raman intensity spectra of Nowotny chimney-ladder semiconducting silicide Ru2Si3 are investigated. The zone-center phonon mode frequencies are found to be in the range 80–510 cm−1. The Born effective charge tensor, oscillator strength and Infrared activity is found to largest for the mode with frequency 422 cm−1 which is primarily contributed by displacements of Si atoms. The largest Raman activity is obtained for mode with frequency 479 cm−1 which is also dominated by vibrations of Si atoms. Modified Becke-Johnson (MBJ) exchange potential is used to compute the band gap of Ru2Si3 which improves the band gap by ∼8% as compared to that obtained using LDA. The computed Infrared reflectivity and Raman intensity spectra are expected to provide benchmark first-principles theoertical results for comparison with the experiments.

Enhanced thermoelectric properties of ASbO3 due to decreased band gap through modified becke johnson potential scheme

Using density functional theory (DFT) calculations, we have explored the effect of Ag and Cs atoms on the electronic transport properties of ASbO3 (A = K, Ag and Cs). We employed first principle calculations for investigation of electronic, optical and thermoelectric properties of ASbO3 compounds. The exchange and correlation potential (EXC) was treated by the modified Becke Johnson functional (mBJ). The optimized lattice constants and internal cell parameters were in agreement with the available experimental data. The self-consistence density of state and band-structure calculations show that Cs-d and Ag-d states remains in valence band and dominate below the Fermi level, while Sb-s/p states mainly contribute in conduction band. When Ag and Cs for K substitution take place, there is a gradual hybridization of Cs-d and Ag-d states results. Optical spectra show the main absorption peak in between 8.0 and 13.0 eV depends on the substituent nature and could be due to transition from hybridized band (Sb-d and Sb-s), below EF to free Ag and Cs-s/p/d states. Frequency-dependent refractive index, n(ω), and the extinction coefficient, k(ω), of ASbO3 were also calculated for the radiation upto 40 eV. We combined the outputs of DFT to transport theory based on Boltzmann equation to calculate the potential use of the ASbO3 as thermoelectrics. The change of the alkaline element affected both of electrical conductivity, Seebeck coefficient and thermal conductivity.

Optoelectronic and thermoelectric response of Ca5Al2Sb6 to shift of band gap from direct to indirect

The structural, optoelectronic and thermoelectric properties of Ca5Al2Sb6 under applied external pressures have been studied using the full potential linear augmented plane wave method. WIEN2k code is used with considering the generalized gradient approximation (GGA), modified Becke–Johnson (MBJ) and modified Becke–Johnson + spin orbit (mBJ + SO) functionals based on density functional theory (DFT). From electronic results, the size of the band gap decreases with increasing pressure and the nature of the band gap shift from direct to the indirect. In high pressure (>35.7 GPa by mBJ + SO), the band gap is also completely disappeared and the nature of compound is changed to the metallic. The calculated anisotropic optical properties such as the static dielectric function, increase with decreasing the size of band gap and increasing of pressure. As a novel result, the thermoelectric performance of n-type and p-type doping of Ca5Al2Sb6 is related to the value of pressure. According to the thermoelectric results, the n-type one has the highest ZT in comparison with the p-type Ca5Al2Sb6 material.

Composition dependent band offsets of ZnO and its ternary alloys

We report the calculated fundamental band gaps of wurtzite ternary alloys Zn1−xMxO (M = Mg, Cd) and the band offsets of the ZnO/Zn1−xMxO heterojunctions, these II-VI materials are important for electronics and optoelectronics. Our calculation is based on density functional theory within the linear muffin-tin orbital (LMTO) approach where the modified Becke-Johnson (MBJ) semi-local exchange is used to accurately produce the band gaps, and the coherent potential approximation (CPA) is applied to deal with configurational average for the ternary alloys. The combined LMTO-MBJ-CPA approach allows one to simultaneously determine both the conduction band and valence band offsets of the heterojunctions. The calculated band gap data of the ZnO alloys scale as Eg = 3.35 + 2.33x and Eg = 3.36 − 2.33x + 1.77x2 for Zn1−xMgxO and Zn1−xCdxO, respectively, where x being the impurity concentration. These scaling as well as the composition dependent band offsets are quantitatively compared to the available experimental data. The capability of predicting the band parameters and band alignments of ZnO and its ternary alloys with the LMTO-CPA-MBJ approach indicate the promising application of this method in the design of emerging electronics and optoelectronics.

First-principles calculations of the electronic and structural properties of GaSb

In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B 0); while for the cohesive energy (E coh), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.

First-principles investigation of electronic properties of Al x In1−x P semiconductor alloy

The modified Becke–Johnson (MBJ) exchange potential together with correlation part of M06 Minnesota functional was used to obtain accurate band structure profile for Al x In1−x P ternary semiconductor alloy. The effective band structures of alloys were calculated using spectral weight approach, and the composition dependence of the fundamental gap energy, critical point energies and electron effective masses were estimated from the weighted average of effective band structures. The results of the supercell calculations for energy gap and bowing parameter are in good agreement with experiments. The results also show that crossover point of (Γ–Γ) direct to (Γ–x) indirect gap energies occurs at x = 0.48, which is consistent with experimental findings. Furthermore, our results show that the combination of MBJ exchange and M06 correlation potential can be used to estimate accurate band structure profile for AlP, InP, and their alloys.

Electronic properties of GaPxAs1-x ternary alloy: A first-principles study

The electronic properties of GaPxAs1-x ternary semiconductor alloy including effective band structures, density of states and effective masses were studied from first principles using supercell (SC) approach. The modified Becke–Johnson (MBJ) exchange potential together with correlation part of both the local density approximation (LDA) and M06 of Minnesota functionals were used to obtain accurate band structure profile. The effective band structures of alloys were calculated using spectral weight approach and composition dependence of the fundamental gap energy and electron effective masses were estimated from it. The results of the supercell calculations for energy gap and bowing parameters for both direct and indirect gaps are in good agreement with the experiments. The results also show that crossover point of (Γ-Γ) direct and (Γ-x) indirect gap energies occurs at x = 0.46, which is in excellent agreement with the experiments. Furthermore, our results show that the combination of MBJ exchange and M06 correlation potential can be used to estimate accurate band structure profile for GaP, GaAs and their alloys.

Pressure Effect on the Electronic Properties of Cerium Monochalcogenides CeX (X=S, Se, Te) Using Modified Becke-Johnson Exchange Potential and LDA+U

We present a systematic and comparative study of the electronic properties of CeX monochalcogenides, The density of state (DOS) and electronic band structure of CeX (X=S, Se, Te) have been calculated using the full-potential linearized augmented plane-wave (FP-LAPW) + local orbital (lo) method based on the density functional theory (DFT), which is implemented in WIEN2k code. The trends in the high pressure behavior of these systems are discussed. Four approximations for the exchange-correlation functional have been used, the GGA's of Perdew-Burke-Ernzherhof. (PBE08) , Engel-Vosko (EV93), a modified version of the exchange potential proposed by Becke and Johnson (MBJ), and LDA+U is used to calculate the band gaps at different pressures. All methods allow for a description of the Ce f electrons as either localized or delocalized, it is found that the underestimations of the bandgap by means of LDA-GGA and Engel-Vosko are considerably improved by using the modified Becke-Johnson (MBJ) potential for all compounds in the series, On the other hand, LDA+U, method gives good results for the lighter chalcogenides, but it fails to give good results for the heavier cerium monochalcogenides.

Theoretical Investigations of the Physical Properties of Cd1−xCaxO Ternary Alloys

The structural, electronic and thermodynamic properties of Cd1−xCaxO ternary alloys are calculated using the first principles calculations performed within the framework of density functional theory. The exchange correlation potential for structural properties is calculated by the standard generalized gradient approximation (GGA) of Perdew et al., while for the electronic properties, the modified Becke-Johnson (MBJ) scheme is also applied. A deviation of the lattice constants from Vegard's law and bulk modulus from linear concentration dependence (LCD) are observed for the alloys. In addition, the thermodynamic stability of the alloys is investigated by calculating the critical temperatures of alloys.

First principles calculations of electronic and optical properties of Ag2S

A theoretical study of structural, electronic and optical properties of Ag2S is presented using the full potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the modified Becke Johnson (MBJ) potential coupled with Local Density Approximation (LDA) was used for the exchange-correlation potential calculation. Ground state properties are determined for the bulk material in monoclinic phase. Band structure reveals that this compound is a direct energy band gap semiconductor. MBJLDA results for the band gap of this compound are much better than those obtained using LDA, Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and Engel–Vosko's GGA (EV-GGA). A very good agreement is observed between MBJLDA band gap and corresponding experimental values as compared to other calculations. Optical constants including the dielectric function, refractive index, extinction coefficient, electron energy loss function, reflectivity and absorption coefficient are obtained and discussed.

Structural, electronic and thermodynamic properties of SrxCd1−xO: A first-principles study

First principles calculations have been performed within the framework of density functional theory to investigate the structural, electronic and thermodynamic properties of SrxCd1−xO ternary alloys. The exchange-correlation potential for structural properties was calculated by the standard local density approximation (LDA) and GGA (PBE), a more accurate nonempirical density functional generalized gradient approximation (GGA), as proposed by Wu and Cohen [Physical Review B 73 (2006) 235116], while for electronic properties, the Engel and Vosko GGA (EVGGA) and the modified Becke–Johnson (MBJ) of the exchange-correlation energy and potential, respectively, are used. Deviation of the lattice constants from Vegard's law and bulk modulus from linear concentration dependence (LCD) were observed for the ternary alloys. The MBJ band gaps values agree well with the available experimental results. In addition the thermodynamic stability of the alloys was investigated by calculating the critical temperatures of alloys.

Full potential calculation of electronic properties of rutile RO 2 (R=Si, Ge, Sn and Pb) compounds via modified Becke Johnson potential

The electronic properties of RO 2 (R=Si, Ge, Sn and Pb; a group IVA element) compounds in rutile structure have been calculated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method. The exchange and correlation (XC) effects are taken into account by an orbital independent modified Becke Johnson (MBJ) potential as coupled with Local Density Approximation (LDA) for all the compounds except for PbO 2 where only Generalized Gradient Approximation (GGA) is considered for the same. We predict a direct band gap in all these compounds with continuous decrease as the atomic size of IVA element increases such that there is an appearance of semimetallic band structure for the last compound, PbO 2. The largest band gap (7.66 eV) has been found for SiO 2, which governs its insulating nature. We observe that MBJLDA results for band gaps of these compounds are far better than those obtained using GGA and Engel–Vosko's GGA (EV-GGA). A very good agreement is observed between MBJLDA band gaps with corresponding experimental values as compared to other calculations. The electronic band structures are also analyzed in terms of contributions from various electrons.