Modified Becke-Johnson Exchange Potential Research Articles

Insights into Ag2Mo3SeO12 for photovoltaic and optoelectronic applications: A theoretical exploration of its structural, electronic, and thermoelectric behavior

The theoretical investigation of the newly discovered quadruple perovskite Ag₂Mo₃SeO₁₂ was conducted using density functional theory (DFT) with the generalized gradient approximation (GGA-PBE) for the structural properties. This study examined the compound's structural, electronic, optical, and thermoelectric properties, utilizing the Tran Blaha modified Becke-Johnson exchange potential (mBJ) for accurate band gap measurement to overcome the bandgap underestimation by GGA-PBE. The stable structure was confirmed through energy-volume optimization and fitted with the Birch-Murnaghan equation of state, using PBE-GGA exchange correlation functional. The findings revealed a band structure with direct transition under the TB-mBJ approach with an energy gap of 1.45 eV. Detailed analyses were conducted, including the density of states and charge density distribution maps. Various optical parameters such as the dielectric function, absorption coefficient, refractive index, and reflectivity were computed, with the static dielectric constant measured at 6.3. Notably, a significant evolution of the absorption coefficient in the visible region highlights the potential of Ag₂Mo₃SeO₁₂ for solar cell and optoelectronic applications. These results pave the way for new photovoltaic material designs. Furthermore, the material demonstrates promising thermoelectric properties with an appropriate figure of merit, Seebeck coefficient, and electrical and thermal conductivity evolution under different temperature conditions, indicating its potential for photovoltaic and optoelectronic applications.

Structural, optoelectronic, and magnetic behaviors of Li2BeTM (TM = V, Cr, Mn, Fe) Se4 compounds using DFT investigations

In this work, we present computational investigations of the electronic, the optical and the magnetic properties of the Li2BeTMSe4(TM = V, Cr, Mn, Fe) compounds using the first-principle calculations based on the density functional theory. In this respect, we employ the generalized gradient approximation corrected by the Tran-Balaha modified Becke-Johnson exchange potential to obtain more accurate results. Among these outcomes, we first study the electronic properties such as the band energy dispersion and the state densities. Regarding this, the Li2BeTMSe4 quaternary family is found to have an indirect band gap of 1.910 eV, 1.905 eV, 2.223 eV and 1.278 eV for TM = V, Cr, Mn, and Fe, respectively. Further, an examination of the optical properties reveals that the computed optical absorption spectra cover a broad energy range in the visible and the ultraviolet spectrums. Motivated by spintronic applications, we additionally determine the total and the local magnetic moments. Then, we compute the associated Curie temperatures via a linear relation with the total magnetic moments. Among others, the Li2BeTMSe4(TM = V, Cr, Mn, Fe) materials involve acceptable temperatures showing potential applications for high temperature nano-devices activities. Comparing the obtained findings with the available ones, the acquired results indicate that the Li2BeTMSe4(TM = V, Cr, Mn, Fe) materials exhibit a wide range of applications in solar cells, optoelectronics, and other fields.

DFT based study of copper calcium halide perovskite nanomaterials for optoelectronic and energy applications

The mechanical, electronic, optical, and thermoelectric analyses of CuCaX3 (X = Cl, Br, I) have been done using DFT based TB-mBJ approach. The stability of CuCaX3 (X = Cl, Br, I) has been confirmed from the enthalpy of formation; values for CuCaCl3, CuCaBr3, and CuCaI3 are −1.07 eV, −1.55 eV, and −2.15 eV, respectively. The phonon spectra plot is also discussed, and the phonon dispersion analysis confirms that the CuCaX3 systems are dynamically stable since no imaginary modes are observed. The modified Becke-Johnson exchange potential is used to evaluate the opto-electronic and thermo-electric properties. By replacing anions (Cl to I), the band gap of the studied material in the visible region has been tailored, from 2.9 eV to 2.65 eV, for renewable energy devices. In addition, various optical properties such as dielectric constant, refraction, absorption, optical conductivity, and optical loss factor have been analyzed for optoelectronic applications. With the replacement of anions (Cl to I), the peaks of maximum intensities shifted to lower energy to values of 7.2 eV, 6.2 eV and 5 eV for CuCaCl3, CuCaBr3 and CuCaI3 respectively. Furthermore, the BoltzTrap code has been used to discuss thermal conductivity, power factor, Hall coefficient, specific capacitance and electron densities in detail for thermoelectric applications. The CuCaX3 family of perovskites has been found to have bandgaps falling in the visible region for light-emitting diodes (LEDs). These also exhibit high thermal efficiency, making them potential multifunctional candidates for optoelectronic and energy harvesting applications.

Structural, magnetic, and optoelectronic properties of rock salt MgO co-doped with Eu-TM (TM = Cu, Ag, and Au) for spintronic and UV detector applications: SP-DFT investigations

This study analyzes how adding europium and transition metals (Cu, Ag, and Au) at a 12.5% concentration to magnesium oxide (MgO) affects its physical characteristics and potential uses. To do so, the full potential linearized augmented plane wave (FP-LAPW) method, based on spin-polarized density functional theory (SP-DFT), is used to derive the results. Wu and Cohen’s generalized gradient approximation (GGA-WC) described the exchange-correlation potential. The modified Becke-Johnson exchange potential (TB-mBJ) was also used to improve the findings of optoelectronic properties. When Eu and TM (Cu, Ag, and Au) impurities are co-doped into the nonmagnetic (NM) semiconductor MgO, the structural optimization results show that the lattice constants increase, and the bulk modulus decreases with increasing the atomic number of transition metals. The resulting dilute magnetic oxides (DMOs) are stable in the spin-polarized ferromagnetic (FM) phase, and the formation energy values confirm their stability in the [Formula: see text] cubic structure, with the lowest value belonging to Eu[Formula: see text]TM[Formula: see text]Mg[Formula: see text]O. Similarly, calculations of electronic properties using the WC-mBJ functional demonstrate that all compounds have an indirect half-metallic bandgap at L-[Formula: see text] equal to 2.53, 2.49, and 1.39 eV for Eu[Formula: see text]Cu[Formula: see text]Mg[Formula: see text]O, Eu[Formula: see text]Ag[Formula: see text]Mg[Formula: see text]O, and Eu[Formula: see text]Au[Formula: see text]Mg[Formula: see text]O, respectively. They have an integer magnetic moment of 6 [Formula: see text]. The density of states shows that at the Fermi level, the 4f-Eu, d-TM, and p-O states give rise to new energy levels. This indicates that the f–p–d hybridization provides this system with its FM properties. Also, these compounds’ dielectric function and absorption spectra are calculated and analyzed to learn more about their optical properties. The results provide insight into the optical behavior of the materials. It is observed that the co-doped compounds exhibit greater optical absorbance than their un-doped MgO counterparts do. This theoretical investigation opens the way to preparing high magnetic moment DMOs using TM and rare earth as dopants suitable for spintronic and UV devices.

First Principle Study of Structural, Electronic, Optical Properties of Co-Doped ZnO

In this theoretical study, the electronic, structural, and optical properties of copper-doped zinc oxide (CZO) were investigated using the full-potential linearized enhanced plane wave method (FP-LAPW) based on the density functional theory (DFT). The Tran–Blaha modified Becke–Johnson exchange potential approximation (TB-mBJ) was employed to enhance the accuracy of the electronic structure description. The introduction of copper atoms as donors in the ZnO resulted in a reduction in the material’s band gap from 2.82 eV to 2.72 eV, indicating enhanced conductivity. This reduction was attributed to the Co-3d intra-band transitions, primarily in the spin-down configuration, leading to increased optical absorption in the visible range. The Fermi level of the pure ZnO shifted towards the conduction band, indicating metal-like characteristics in the CZO. Additionally, the CZO nanowires displayed a significant blue shift in their optical properties, suggesting a change in the energy band structure. These findings not only contribute to a deeper understanding of the CZO’s fundamental properties but also open avenues for its potential applications in optoelectronic and photonic devices, where tailored electronic and optical characteristics are crucial. This study underscores the significance of computational techniques in predicting and understanding the behavior of doped semiconductors, offering valuable insights for the design and development of novel materials for advanced electronic applications.

Electronic structure calculations on copper substituted silver iodide through modified Becke-Johnson exchange potential

Silver iodide (AgI) has a rich phase diagram with the γ-AgI being one of the forms. γ-AgI is a n-type semiconductor that crystallizes into zinc blende structure and found to be stable at ambient temperature and pressure. The electrical transport in γ-AgI is mediated by the migration of Ag+ cationic interstitial defects, while the Cu + Frenkel defects are responsible for the conduction in γ-CuI, a p-type semiconductor. This intrigues to understand the transition of the nature of electrical transport with the replacement of Ag by Cu. In this regard, we report the computational study on the Cu substituted γ-AgI using the density functional theory (DFT) with Tran-Blaha modified Becke-Johnson (TB-mBJ) scheme. The calculations are performed on γ-Ag1-xCuxI (x = 0.00–1.00) supercell through full potential linearized augmented plane wave (FP-LAPW) method. The lattice parameter and bulk modulus are found to vary nearly linear with copper concentration x, whereas band gap values follow a non-linear variation.

Tailoring the photocatalytic properties of anatase TiO2 by B–TM (TM = Pt, Ta, V) co-doping

In order to provide insight into the influence of co-doping with boron (B) and transition metals (TM = Pt, Ta, V) on the photoactivity of anatase TiO2, the electronic, structural and optical characteristics of the mentioned co-doped systems were studied using density functional theory calculations and the modified Becke–Johnson exchange potential. For each transition metal two cases were considered, with B atom either replacing O atom (B-substitutional) or imbedding interstitially (B-interstitial) into TiO2 lattice. The calculations showed that the co-doping is more favorable for the B-interstitial systems than for the B-substitutional ones and under the O-rich conditions. For the B-substitutional cases a slight decrease of the band gap is observed. In contrast, the results obtained for the B-interstitial systems exhibited no band gap narrowing. However, in these systems, the occurrence of localized states within the band gap is noticed, which could improve visible light absorption through a two-step optical transition.

Ab-initio investigations for structural, optoelectronic and thermoelectric properties of Li2BeXSe4 (X = Ge, Si, Sn) compounds

Motivated by photovoltaic activities, we study certain aspects of the stannite structure (ST) of the Li2BeXSe4 (X = Ge, Si, Sn) compounds using the full potential augmented plane wave approach implemented in the Wien2k code. Concretely, we use the generalized gradient approximation (GGA) and the modified Becke–Johnson exchange potential (mBJ) to evaluate in a precise way, the band gaps, the total and the partial densities, as well as the optical and the thermoelectric properties. Among others, we show that the Li2BeXSe4 (X = Ge, Si, Sn) semiconductors exhibit a direct band gap in the Γ point of the Brillouin Zone (BZ). Furthermore, the optical properties of the three compounds show a strong optical conductivity and a good optical absorption. As a result, we reveal that the proposed materials are suitable for the application in photovoltaic solar cells. Using the BoltzTrap package, we also examine and discuss the thermoelectric properties such as the Seebeck coefficient (S), the electrical conductivity, and the thermal conductivity as a function of the temperature. We find that the Li2BeXSe4 (X = Ge, Si, Sn) compounds exhibit good thermoelectric transport properties, making them a good candidates for clean energy applications.

First-principles calculations to investigate structural, electronic, and optical properties of zinc-blende CdxMg(1-x)TeyS(1- y) matched to CdX (X= S, Te) for Predicting critical thickness and corrective Term's effect

We report in the present paper ab initio calculations of the structural, electronic and optical properties of zinc blende quaternary alloys CdxMg(1-x)TeyS(1-y) lattice matched to CdX (X = S, Te) exploring the density functional method within the generalized gradient approximation (GGA). From the obtained values of the ground state energy, we have determined the structural parameters and the band gap energies. We found an underestimation of the gap energies obtained for both (GGA-PBE) and the Modified Becke-Johnson exchange potential (TB-mbJ) approximations for the CdS, CdTe, MgS, and MgTe. Even though mbJ significantly corrects the energy gaps, it is no longer valid to properly reproduce the exchange-correlation potential. Consequently, we tend to use the corrective term ΔE to exploit it to enhance the electronic band structures.Moreover, we have reported the concentration depending on the refractive index and the dielectric function using (mbJ). The critical thickness, for which the lattice of the CdxMg(1-x)TeyS(1-y) matches CdS and CdTe, respectively, are determined. The results show that for all Cd and Te incorporated amounts, the CdxMg(1-x)TeyS(1-y) lattice matched to CdX (X = S, Te) substrate alloys exhibits a semiconducting behavior with a small lattice mismatching ratio which might make CdxMg(1-x)TeyS(1-y)/CdX materials promising and useful for optoelectronic applications.

Energy Bandgap of Cd1−xZnxTe, Cd1−xZnxSe and Cd1−xZnxS Semiconductors: A First-Principles Analysis Based on Tran–Blaha–Modified Becke–Johnson Exchange Potential

Energy Bandgap of Cd1−xZnxTe, Cd1−xZnxSe and Cd1−xZnxS Semiconductors: A First-Principles Analysis Based on Tran–Blaha–Modified Becke–Johnson Exchange Potential

Effect of hydrostatic strain on the mechanical properties and topological phase transition of bi-alkali pnictogen NaLi2Bi

The bi-alkali pnictogens have attracted significant attention for optoelectronic and photocathodic device applications. However, in most of the compounds belonging to this family, there has been less effort put into investigating the mechanical properties and topological phase transitions (TPT) of the compounds. Here, in the framework of density functional theory, the mechanical properties and topological phase transition of NaLi2Bi under hydrostatic pressures are investigated. Elastic constants and phonon calculations have shown the mechanical and dynamical stability of this compound under hydrostatic tension and compression. The analysis of the elastic constants show that the NaLi2Bi in the equilibrium state is an auxetic material with a negative Poisson’s ratio of -0.285, which changes to a material with a positive Poisson’s ratio under hydrostatic tension. Meanwhile, Poisson’s ratio and Pugh ratio indicate that this compound has brittle behavior and maintains it under hydrostatic pressures. The calculated results of the band structure within the generalized gradient approximation (GGA) (Tran-Blaha modified Becke-Johnson exchange potential approximation (TB-mBJ)) show that NaLi2Bi is a nontrivial topological material (trivial topological material). It was found that hydrostatic compression (tension) in the GGA (TB-mBJ) approach leads to a transition from a nontrivial (trivial) to a trivial (nontrivial) topological phase for this compound. Moreover, the calculated Wannier charge centers confirm the TPT. Identifying the mechanisms controlling the auxetic behavior and TPT of this compound offers a valuable feature for designing and developing high-performance nanoscale electromechanical and spintronic devices.

DFT investigations of optoelectronic and thermoelectric properties of stannite phase of Cu2SrXSe4 (X = Ge, Si, Sn) compounds using TB-mBJ mechanism

Using the density functional theory (DFT) computations implemented in WIEN2K package and Boltzmann theory with the BoltzTrap code, we study certain physical properties of a new class of Cu2SrXSe4 (X = Ge, Si, Sn) materials. Concretely, we investigate the electronic, the optical and the thermoelectric aspects of such materials from the generalized gradient approximation (GGA) corrected by the Tran Balaha modified Becke–Johnson exchange potential (GGA+TB-mBJ). Analyzing the computed electronic properties, we show the semiconducting nature of these compounds. Precisely, we reveal that these compounds involve an indirect band gap with p type. This electronic aspect is very important for the absorber solar cell layers due to the fact that the length diffusion of the electron is larger than the one of the hole. We find that the obtained gap values of such a new family inspired by CZTS materials can be compared with various absorber layers. For the Cu2SrSnSe4 model, we observe similar behaviors compared to the silicon solar cell absorber layers. Using the scalar dielectric function, we investigate the optical properties of the studied materials. Precisely, we obtain that such a family of materials involve higher values of the absorption coefficient in the visible and the ultra violet light spectrum. For each material, we observe that the absorption starts at the corresponding band gap energies. Exploiting Boltzmann theory with the BoltzTrap code, we compute and examine the thermoelectric properties such as the Seebeck coefficient, the thermal conductivity, the electrical conductivity, and the figure of merit as a function of the temperature. As a result, we show that the studied materials involve a high absorption spectra and a good figure of merit (ZT) showing relevant features for photovoltaic and thermoelectric applications.

Electronic and optical properties of the R3 Ni3TeO6 compound described by the modified Becke-Johnson exchange potential

Calculations based on the density functional theory (DFT) have been realized to study the electronic and optical properties of the Ni3TeO6 compound with a hexagonal crystal structure (R3 space group). Exchange and correlation electronic effects were described by a modified Becke-Johnson (mBJ) potential in its semiconductor variance form. The collinear antiferromagnetic state of the R3 Ni3TeO6 compound was simulated. The calculated spin magnetic moment of the Ni atoms (1.65 μB) was found to be in good agreement with the experimental result (2.03 μB). Moreover, the calculated optical band gap (2.8 eV) agreed well with the experimental prediction (2.5 eV). These facts suggest a reliable electronic structure description of the material. Hence, we also calculated the complex dielectric function, optical absorption spectrum, refractive index, and extinction coefficient. The optical absorption spectrum was interpreted based on the determined electronic structure. The direct optical absorption edge of the material was characterized by the electronic transitions from O 2p states to Te 5s states and from Ni 3d states to O 2p states. This description did not agree with previous ones based on DFT + U calculations or those made based on the electronic structure of the Ni3V2O8 compound. Thus, an alternative description of the electronic structure of the R3 Ni3TeO6 compound in its antiferromagnetic state using the DFT + mBJ calculations has been suggested, and consequently a new origin for the optical absorption observed around the optical band gap.

Investigation of the Optoelectronic and Photovoltaic Properties of YxIN1-xP Alloys using First Principles Calculations

Abstract Structural stability, electronic, optical, and photovoltaic properties of pure and doped InP were evaluated by using first principles calculations via the density functional theory (DFT). The exchange-correlation potential is treated with generalized gradient approximation (GGA-PBE). Additionally, the Tran Blaha modified Becke-Johnson exchange potential (TB-mBJ) is employed, because it gives very accurate results of the band gap in solids. Our results reveal that all compounds are energetically and mechanically stable. It is found that for Y concentrations less than 30%, the favored structure is a Zinc blende-like one, while for Y concentrations greater than 30%, the favored structure is a NaCl-like structure. The substitution of In by Y is found to be able to enlarge the direct bandgap of about 34% (from 1.43 eV to 2.17 eV) and confirms the semiconductor behavior for zinc blende stable structures. The absorption coefficient is reasonably exceeding 105 cm −1 for YxIn1-xP alloys in the case (x=0 and x=25%). The reflectivity shows less than 30% around the energy value of 2 eV and an efficiency of solar cell of 18% can be achieved for Y0.25In0.75P. Also, a thickness of L = 1μm is enough to confirm the experimental data. Regarding to the matching of lattice parameters (a mismatch < 4%) of InP and Y0.25In0.75P and the band gap energy difference made Y0.25In0.75P suitable for optoelectronic and photovoltaic devices in particularity as Tandem solar cells (Y0.25In0.75P/InP) and quantum well (Y0.25In0.75P/InP/Y0.25In0.75P) applications. In the absence of experimental works, our results can be useful for further studies.

Theoretical prediction of doping iron ions effect on the optoelectronic and magnetic cobalt-based perovskite (Co1-xFexScO3)

The ab-initio framework has taken place by means of the Full-potential Linear Augmented Plane-Wave (FP-LAPW) method, using the modified Becke-Johnson exchange potential approximation. This modified method was carried out to study the effects of doping iron ions on the structural, electronic, magnetic, and optical properties of CoScO3 perovskite compound. Doping Fe ions have formed a nonstoichiometric perovskite Co1-xFexScO3 where x = 0, 0.25, 0.50, 0.75, and 1. all doped compounds crystallized in a tetragonal lattice due to the Jahn-Teller effect, while the lattice constant was calculated and found to vary between the value of the two pure compounds. Meanwhile, the stabilities of the studied compounds are shown in the negative values of the formation energy. The magnetic moment was calculated and the whole compounds showed a ferromagnetic behavior. Co1-xFexScO3 perovskite is a potential candidate for spintronic application due to the presence of the half metallic behavior. All optical spectrums including dielectric function, absorption coefficient, reflectivity and refractivity index, and energy loss function show remarkable features for the proposed perovskites.

First-principles WC-GGA and mBJ calculations for structural, electronic, optical and elastic properties of MxGa1-xSb (M=Al, In, B) ternary alloys

GaSb based ternary alloys have indicated wide range variations in physical, electronic and optical properties. In the present study the structural, electronic, optical and elastic properties of MxGa1-xSb (M = Al, In, B) ternary alloys have been reported and discoursed based on the first-principles investigation. The current work attempts to provide an insight into the evolution of electronic, optical and elastic properties of ternary alloys of MxGa1-xSb (M = Al, In, B) with variation in their constituent compounds. Density functional theory (DFT) operation based on the augmented plane wave + local orbitals (APW + lo) method has been employed to estimate the structure, density of states (DOS), bandstructure, optical and the elastic properties of ternary alloys MxGa1-xSb (M = Al, In, B) for (x = 0, 0.25, 0.50, 0.75, 1) compositions. Computations were performed using the exchange-correlation energy functional from Wu-Cohen, a generalized-gradient approximation (WC-GGA) as well as the original modified Becke-Johnson exchange potential (mBJ) available with the WIEN2k code. As WC-GGA has been observed to underestimate the bandgap, the bandstructure of ternary alloys MxGa1-xSb (M = Al, In, B) for (x = 0, 0.25, 0.50, 0.75, 1) compositions has been reported using modified Becke-Johnson exchange potential (mBJ) method. In case of AlxGa1-xSb and BxGa1-xSb alloys, the bandgap values have been observed to deviate strongly from the Vegards law indicating the existence of a bowing parameter while the bandgap values of InxGa1-xSb alloys are in excellent agreement with the reported values and deviate marginally from the Vegards law. Further the optical properties, real and imaginary parts of ϵ(ω) and loss function of MxGa1-xSb (M = Al, In, B) for ternary alloys have been calculated using WC-GGA. The critical points, peaks and shoulders of imaginary part of dielectric function in these alloys have been reported. The elastic properties of these alloys, Bulk modulus (B), Shear modulus (G), Young modulus (E) and Poisson's coefficient (ν) have also been calculated using the Cubic-elastic and Tetra-elastic packages.

Stibnite at modified Becke-Johnson exchange potential

The demand for cheaper, nontoxic and earth-abundant materials as absorbing layer for solar cell is immensely needed to replace scarce, toxic and expensive one. In this regard, chalcogenide materials have considerably attracted the attention of a lot of researchers because of showing a great potential for different applications. Stibnite (Sb2S3), a chalcogenide binary material is intensively investigated for exploiting its potential for different energy technologies being a less toxic, abundantly available, stable and efficient one, which are the fundamentals for sustainability as well as to realize the dream of green energy. In this study, a computational study of the structural, electronic and optical properties of the stibnite (Sb2S3) crystal structure is presented using the full potential (FP) linearized augmented plane wave (LAPW) method framed within the density functional theory (DFT). For the estimation of the exchange-correlation potential part, besides the local density approximation (LDA), Wu-Cohen parameterized generalized gradient approximation (WC-GGA) Perdew-Burke-Ernzerhof parameterized generalized gradient approximation (PBE-GGA), and Perdew-Burke-Ernzerhof generalized gradient approximation for solids and surfaces (PBEsol-GGA), the Trans-Blaha approach of the modified Becke-Johnson (TB-mBJ) potential is used to improve the fundamental band gap value. Moreover, these calculations are performed by involving spin-orbit coupling (SOC) contribution as well. Additionally, optical properties, such as imaginary and real parts of the dielectric function, optical conductivity absorption coefficient, refractive index, reflectivity, and electron energy loss function were investigated as well. The obtained results of the band gap energy and optical properties with TB-mBJ potential were found closer to the experimental data and endorse its potentiality for the photovoltaics applications.

First-principles calculations to investigate structural, electronic and phonon properties of sodium bromide (NaBr) and sodium iodide (NaI) crystals

In this paper, the first-principles study is performed to calculate the structural, electronic and phonon properties of alkali halides NaBr and NaI. The calculations for structural and electronic properties have been carried out using the full-potential linearized augmented plane-wave (FP-LAPW) method that is employed in the WIEN2k code, whereas the phonon properties are studied using the Quantum Espresso program based on density-functional theory within plane-wave fundamental sets and pseudo-potentials approaches. The calculation of structural, electronic band properties were carried out using generalized gradient approximation (GGA), local-density approximation (LDA) and a combination of modified Becke-Johnson exchange potential with LDA and GGA (TB-mBJ-GGA/LDA) for exchange-correlation potential. The calculated structural parameters are in good agreement with experimental results. In our electronic calculations, the obtained bandgaps are underestimated by LDA and GGA functionals compared to empirically derived results, which is an expected result. However, the calculated bandgaps by the modified Becke-Johnson exchange potential are in perfect agreement with the experiment. Finally, the dynamic properties of NaBr and NaI compounds were investigated. Both phonon dispersion and phonon density of states curves were calculated for compounds along with the high symmetry directions in the Brillouin region. The dynamical properties of NaBr and NaI crystals are analyzed and discussed.

Investigation of the electronic, structural, optical and thermoelectric properties of ternary chalcopyrite ACuS2(A=Al, Ga and In): Ab initio study

In the present work, the structural, electronic, optical and thermoelectric properties of the ternary chalcopyrite compounds defined by ACuS2(A=Al, Ga, In) has been performed by density functional theory (DFT) combined with Boltzmann transport theory. Based on the generalized gradient (GGA) approach, the stability accompanied with the structural parameters of the studied structure compounds was evaluated. Furthermore, modified Becke-Johnson exchange potential (TB-mBJ) was adopted for the exchange correlation potential in order to prove the electronic and optical features of ACuS2(A=Al, Ga and In). The plotted density of state, band structure, distribution charge density of the ACuS2(A=Al, Ga and In) component, with dielectric function, reflectivity, Seebeck coefficients, electrical and thermal conductivity are obtained and discussed. Our result reveal, for electronic properties, that all components exhibit p-type semiconductor with direct band gap, with 1.51 eV for GaCuS2. The chemical bonding analysis shows the presence of ionic bonding between Al/In/Ga and S. The calculated dielectric function and the absorption coefficient indicate that InCuS2 followed by GaCuS2 display an excellent absorption in the visible range with low reflectivity. The evaluated results are in excellent agreement with available experimental and theoretical data. The physical properties of the novel ACuS2 (A=Al, Ga and In) compound show promising candidate toward photovoltaic, optoelectronic and thermoelectric device.

Performance of the modified Becke–Johnson potential employing the pseudopotential plane-wave approach for band structure calculations

The modified Becke–Johnson exchange potential combined with local-density approximation correlation (mBJLDA) has recently attracted interest because it provides highly improved band gaps at a very low computational cost. In this work we performed an extensive investigation of the performance of the mBJLDA potential employing a norm-conserving pseudopotential plane-waves approach (mBJLDA@PP), as implemented in the abinit code, using a test set of 83 solids representing a wide range of semiconductors and insulators. Our results confirm the conclusion of our previous study that the number of electrons treated as valence in the pseudopotentials of the cations can have a significant impact on the calculated mBJLDA@PP band gaps. More specifically, while the use of typical pseudopotentials leads to accurate band gaps of certain systems, it yields significantly underestimated band gaps for other systems compared to experiment and to those of the all-electron mBJLDA (mBJLDA@AE) approach. The classes of the latter systems are identified, and this problem is resolved by including some outer core states as valence. The resulting mean absolute error in the calculated band gaps (compared to experiment) is of 0.46 eV, which is comparable to that of the mBJLDA@AE band gaps, reflecting the accuracy and reliability of the mBJLDA@PP approach for the band gap calculations.