Engel Vosko Generalized Gradient Approximation Research Articles

Iridium's influence on the structural, electronic and mechanical characteristics of ZrCo1-xIrxSb half-heusler alloys

Structural, electronic and mechanical properties ofZrCo1−xIrxSbHalf-Heusler alloys with varying x concentrations (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1) were studied by performing the exchange-correlation (XC) energy evaluated using the local density (LDA) and generalized gradient (GGA) approximations. The calculated lattice constant, bulk modulus, and band gap energy of the ternary alloy show good agreement with previous theoretical predictions. The results indicate that an increase in Ir atom concentration in the alloy leads to an enlargement of the lattice constant (from 6.10 to 6.36 Å) and bulk modulus (from 138.09 to 149.70 GPa), resulting in increased volume and hardness of the compound. Moreover, the Engel-Vosko generalized gradient approximation (EVGGA) and modified Becke-Johnson (mBJ) schemes were employed to improve the calculations of the band structure and density of states. The studied alloys exhibit semiconductor characteristics, with a direct band gap for both x = 0.75 and x = 0.875 concentrations and an indirect band gap for the rest of the concentrations. The computed elastic constants for ZrCo1−xIrxSb alloys satisfy the requirements for mechanical stability. The VRH approximations have been used to determine the bulk modulus, shear modulus, Young's modulus, Poisson's ratio and Hardness. In addition, we also determined the anisotropy factor, sound velocities and Debye temperature.

Theoretical Investigation of Structural, Electronic, and Optical Properties of ZnSnP2 Semiconductor

Abstract The structural, electronic, and optical properties of ZnSnP2 compound were determined using the first principles calculations. We applied the full-potential enhanced plane wave method (FP-LAPW) within the framework of density functional theory (DFT) as implemented in the Wien2k package. The exchange-correlation potential term was treated using the local density approximation (LDA), the generalized gradient approximation (GGA), the Engel–Vosko generalized gradient approximation (EV–GGA) and GGA plus modified Becke– Johnson (mBJ). The lattice parameters of the ZnSnP2 obtained by minimizing the total energy are consistent well with the existing theoretical and experimental results. The Dugdale and MacDonald Grüneisen parameter was found to be 1.43 from the GGA and 1.44 from the LDA, respectively. According to the electronic properties, the band structure analysis of ZnSnP2 shows that it has a direct band gap in the (Γ-Γ) direction with a value of 1.43 eV. We have investigated the optical properties of ZnSnP2 semiconducting compound. The data of the dielectric functions shown that the peaks are positioned at around 2.41, 3.21, 3.83 and 4.09 eV, respectively.

Optical Properties of ZnS and Effect of Doping with Transition Elements

By the help of density functional theory for a Cu doped ZnS compound the charge density,Fermi surface and electronic structure have been examined. We have used (FP-LAPW)method, to deal with interchange relationship potential for solving of kohn-sham equations.We apply generalized gradient approximation (GGA), local density approximation (LDA)and Engel-Vosko GGA (EVGGA). Cu doped ZnS compound confirms that nature ofmaterial is metallic and Fermi energy (EF) is obtained by the overlapping of Cu-p and Znd state. At Fermi energy (EF) calculated density of states is 51.932, 18.655 and 13.235 states/ev, and low-temperature electronic specific heat co-efficient (?) is found to be9.008mJ/mol-K2 for GGA, 3.236mJ/mol-K2 for LDA, and it was 2.295mJ/mol-K2 forEVGGA respectively. The thermal properties and optical constant were also discussed andcalculated.

Ab initio calculations of antimony sulphide nanowire

We have performed first-principles calculations on orthorhombic antimony sulphide (Sb2S3) nanowire using full-potential linearized augmented plane wave (FP-LAPW) method based on the density-functional theory (DFT) as implemented in WIEN2k package to investigate the electronic and optical properties. Engel–Vosko generalized gradient approximation (EV-GGA) is used as exchange-correlation functional. The nanowire is simulated in the [001] direction with vacuum in two directions using supercell method. The results are compared with Sb2S3 bulk results obtained in our pervious study. We have found that the electronic and optical properties significantly change in Sb2S3 nanowire. The density of state (DOS) for Sb2S3 nanowire calculated is higher than bulk Sb2S3 and from the electronic band structure, the indirect band gap is about 0.12 eV where this value is much lower than Sb2S3 bulk. However, this value is much lower than experimental value. The optical properties including absorption coefficient, reflectivity, refractive index and energy loss function are derived from the calculated complex dielectric for photon energy up to 20 eV to understand the optical behavior of Sb2S3 in one-dimensional (1-D) nanostructure. From analysis, the optical response of Sb2S3 nanowire demonstrate quite interesting optical behavior for one-dimension (1-D) nanostructure. The absorption coefficient for Sb2S3 nanowire is considerably higher in visible light range than Sb2S3 bulk.

First-principles calculations of antimony sulphide Sb2S3

The structural, electronic and optical properties of Sb2S3 have been investigated using full-potential linearized augmented plane wave method within density functional theory (DFT) framework, treating exchange-correlation potential with Engel-Vosko generalized gradient approximation (EV-GGA). Electronic properties calculations were performed with and without taken into account the effects of spin-orbit coupling (SOC) . From our results we found that structural properties,density of states and band structure are in good agreement with experimental results.The effects of SOC and relativistic on electronic properties were found to be negligible. However, optical properties, namely, imaginary and real parts of dielectric function, reflectivity, absorption coefficient, refractive index, extinction coefficient and energy loss function were calculated and analyized.Optical gap of 1.61 eV proves that Sb2S3 metal chalcogenides is a promising material for solar cell device.

Engel-Vosko GGA calculations of the structural, electronic and optical properties of LiYO2

Structural, electronic and optical properties of lithium yttrium oxide (LiYO2) are investigated using density functional theory (DFT). These calculations are based on full potential linearized augmented plane wave (FP-LAPW) method implemented by WIEN2k. The generalized gradient approximation (GGA) is used as an exchange correlation potential with Perdew-Burk-Ernzerhof (PBE) and Engel-Vosko (EV) as exchange correlation functional. The structural properties are calculated with PBE-GGA as it gives the equilibrium lattice constants very close to the experimental values. While, the band structure and optical properties are calculated with EV-GGA obtain much closer results to their experimental values. Our calculations confirm LiYO2 as large indirect band gap semiconductor having band gap of 5.23eV exhibiting the characteristics of ultrawide band gap materials showing the properties like higher critical breakdown field, higher temperature operation and higher radiation tolerance. In this article, we report the density of states (DOS) in terms of contribution from s, p, and d-states of the constituent atoms, the band structure, the electronic structure, and the frequency-dependent optical properties of LiYO2. The optical properties presented in this article reveal LiYO2 a suitable candidate for the field of optoelectronic and optical devices.

Theoretical study of structural, electronic and optical properties of BaxPb1−xS, BaxPb1−xSe and BaxPb1−xTe ternary alloys using FP-LAPW approach

The structural, electronic and optical properties of BaxPb1−xS, BaxPb1−xSe and BaxPb1−xTe alloys for 0 ≤ x ≤ 1 in their rock-salt (B1) crystallographic phase have been calculated using the full-potential linearized augmented plane wave (FP-LAPW) method under the framework of density functional theory (DFT). Using the Wu-Cohen generalized-gradient approximation (WC-GGA) parameterization scheme, ground-state structural parameters such as equilibrium lattice constants, bulk modulus and its pressure derivatives are calculated and deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence have been observed for the alloys. Electronic band structures and density of states have been calculated using Tran-Blaha modified Becke-Johnson (TB-mBJ) parameterization scheme to study the electronic properties of the binary compounds and their ternary alloys. In addition, Engel-Vosko generalized gradient approximation (EV-GGA) and WC-GGA induced energy band gaps have also been calculated for comparison. Using the approach of Zunger and co-workers, the microscopic origins of band gap bowing have been discussed in term of volume deformation, charge exchange and structural relaxation. Optical properties of the binary compounds and their ternary alloys have been calculated in terms of their respective dielectric function, refractive index, reflectivity and optical conductivity. Few calculated results are compared with available experimental and other theoretical data.

Revealing the electronic structure and optical properties of K6[Mo4O8F10] novel molybdenum oxyfluoride materials

The electronic structure and optical properties of the molybdenum oxyfluoride K6[Mo4O8F10] single crystal were investigated. Based on X-ray diffraction data, the crystal structure was optimised so as to minimise the forces acting on each atom. The calculation reveal that K6[Mo4O8F10] is an indirect band gap semiconductor of about 1.51 eV, using the local density approximation, 1.72 eV, using gradient approximation (PBE-GGA), 1.81 eV using Engel–Vosko generalized gradient approximation and 2.01 eV, from the recently modified Becke–Johnson potential (TB-GGA-mBJ). Partial density of states reveals the orbitals’ contribution and the degree of the hybridisations between the orbitals. The contours of the valence electronic charge density of each atom in K6[Mo4O8F10] reveal that there are some electrons from Mo, K, F and O orbitals that are transferred to the valence bands and participate in the interactions between the Mo, K, F and O atoms to form covalent bonding. The strength of the covalent bond depends on the degree of the hybridisation and the electro-negativity differences between Mo, K, F and O atoms. The calculated bond lengths exhibit good agreement with the experimental data. The optical properties help to get deep insight into the electronic structure and reveal the types of the orbitals that participate in the optical transitions. It has been found that the investigated crystal possesses negative uniaxial anisotropy (δε = −0.102) and positive birefringence ( = 0.2765).

Electronic, magnetic and thermal properties of Co2CrxFe1−xX (X=Al, Si) Heusler alloys: First-principles calculations

Density functional theory (DFT) based on the full-potential linearized augmented plane wave (FP-LAPW) method is used to investigate the structural, electronic, magnetic and thermal properties of Co2CrxFe1−xX (X=Al, Si) full Heusler alloys, with L21 structure. The structural properties and spin magnetic moments are investigated by the generalized gradient approximations (GGA) minimizing the total energy. For band structure calculations, GGA, the Engel–Vosko generalized gradient approximation (EVGGA) and modified Becke–Johnson (mBJ) schemes are used. Results of density of states (DOS) and band structures show that these alloys are half-metallic ferromagnets (HMFS). A regular-solution model has been used to investigate the thermodynamic stability of the compounds Co2CrxFe1−xX that indicates a phase miscibility gap. The thermal effects using the quasi-harmonic Debye model are investigated within the lattice vibrations. The temperature and pressure effects on the heat capacities, Debye temperatures and entropy are determined from the non-equilibrium Gibbs functions.

First principles study of hydrogen storage material NaBH4 and LiAlH4 compounds: electronic structure and optical properties

A comprehensive study of structure, phase stability, optical and electronic properties of LiAlH4 and NaBH4 light-metal hydrides is presented. The calculations are carried out within density functional theory using the full potential linear augmented plane wave method. The exchange-correlation potential is treated within the local density approximation and the generalized gradient approximation (GGA) to calculate the total energy. Furthermore, the Engel–Vosko GGA approach is employed to compute electronic and optical properties such as reflectivity spectra. The phases α, β and γ of LiAlH4 and NaBH4 hydrides are investigated, the phase transition from the β to the high-pressure γ phase is determined for NaBH4 and is accompanied by a 1% volume decrease. For LiAlH4, no phase transition is detected. The materials under consideration are classified as wide band gap compounds. From the analysis of the structures at different phases, it is deduced that the hydrides show strong covalent interaction between B (Al) and H in the [BH4]− ([AlH4]−) anions and ionic bonding character between [BH4]− and Na+ for NaBH4, and [AlH4]− and Li+ for LiAlH4. The complex dielectric function, absorption coefficient and the reflectivity spectra are also computed and analyzed in different phases.

Electronic properties and topological phases of ThXY (X = Pb, Au, Pt and Y = Sb, Bi, Sn) compounds

The electronic properties and topological phases of ThXY (X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn) compounds in the presence of spin–orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases (insulator or metal) and normal phases within generalized gradient approximation (GGA) and Engel–Vosko generalized gradient approximation (GGA_EV) are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths–pressure curves.

DFT calculations for the electronic structure of alpha phase of CsMgH3 as advanced hydrogen storage materials

Detail analyzes to the electronic structure of magnesium based ternary metal hydrides containing alkali and alkaline-earth elements (α-CsMgH3) is reported so as to justify its use as advanced hydrogen storage systems. Calculations based on full-potential method within several exchange correlation potentials are performed to gain a reliable results. It has been found that α-CsMgH3 exhibits indirect band gap of about 2.3 eV (local density approximation -LDA), 2.6 eV (generalized gradient approximation -PBE-GGA), 2.9 eV (Engel-Vosko generalized gradient approximation - EVGGA) and 3.2 eV (recently modified Becke-Johnson potential -mBJ). The electronic band structure and the density of states reveal that at the energy regions around −5.0 eV and from −3.5 eV up to −2.0 eV the H-1s state hybridized with Mg-3s state to form a peak at around −5.0 eV and three peaks between −3.5 eV and −2.0 eV. The energy region from −2.0 eV up to Fermi level is originated by the interactions between H-1s and Mg-2p states. Thus, the interactions between the orbitals of H and Mg atoms leads to form strong covalent bonding between H and Mg atoms. The conduction bands are mainly originated from the empty states of Cs and partially from Mg-3s/2p states, while H-1s has insignificant contribution to the empty states. The chemical bonding were analyzed in term of charge density and charge transfer, we found that a charge transfer towards H atom occur. To gain further insight for deeply understanding the electronic structure, the optical dielectric functions are calculated based on the calculated band structure.

Engel–Vosko generalized gradient approximation within DFT investigations of optoelectronic and thermoelectric properties of copper thioantimonates(III) and thioarsenate(III) for solar‐energy conversion

The electronic structure and optical properties of Rb2Cu2Sb2S5, Cs2Cu2Sb2S5, and Rb8Cu6As8S19 were investigated from first principles based on Engel–Vosko generalized gradient approximation (EV‐GGA). The calculated band structures and density of states confirm that these compounds have an indirect bandgap. The bands near the Fermi level were mainly contributed from Cu‐3d states along with a small participation of S‐3p states. The partial density of states shows that Cs and Rb elements are bonded ionically to sulfur, whereas Cu, Sb, As, and S element show covalent bonds with each other. From the electronic structure and using EV‐GGA, the frequency‐dependent optical parameters such as the real and imaginary parts of the dielectric functions, energy loss function, and reflectivity were calculated. These optical parameters prove that these compounds are potentially interesting for the field of optoelectronic and optical devices. The temperature‐dependent thermoelectric properties such as the electrical conductivity, Seebeck coefficient, thermal conductivity, and power factor were calculated based on combination of DFT output and Boltzmann transport theory.

First-principles calculations for optical investigations of PbX (X = S, Te) compounds under quantum dots diameter effect

The full potential-linearized augmented plane wave (FP-LAPW) method is implemented in WIEN2K code to calculate the indirect energy gap (Γ–X) using density functional theory. The Engel–Vosko generalized gradient approximation (EVGGA) and modified Becke–Johnson (mBJ) formalisms are used to optimize the corresponding potential for energetic transition and optical properties calculations of PbS and PbTe compounds as a function of quantum dot diameter and are used to test the validity of our model of quantum dot potential. The refractive index and optical dielectric constant are investigated to explore best applications for solar cells. The calculated results are in agreement with other experimental and theoretical data.

Engel-Vosko GGA Approach Within DFT Investigations of the Optoelectronic Structure of the Metal Chalcogenide Semiconductor CsAgGa2Se4

Metal chalcogenide semiconductors have a significant role in the development of materials for energy and nanotechnology applications. First principle calculations were applied on CsAgGa2Se4 to investigate its optoelectronic structure and bonding characteristics, using the full-potential linear augmented plane wave method within the framework of generalized gradient approximations (GGA) and Engel-Vosko GGA functionals (EV-GGA). The band structure from EV-GGA shows that the valence band maximum and conduction band minimum are situated at Γ with a band gap value of 2.15 eV. A mixture of orbitals from Ag 4p 6/4d 10, Se 3d 10, Ga 4p 1, Se 4p 4 , and Ga 4s 2 states have a primary role to lead to a semiconducting character of the present chalcogenide. The charge density iso-surface shows a strong covalent bonding between Ag-Se and Ga-Se atoms. The imaginary part of dielectric constant reveals that the threshold (first optical critical point) energy of dielectric function occurs 2.15 eV. It is obvious that with a direct large band gap and large absorption coefficient, CsAgGa2Se4 might be considered a potential material for photovoltaic applications.

Elastic, Electronic, Optical and Thermal Properties of Na2Po: An Ab Initio Study

The structural, elastic, electronic, optical and thermodynamic properties of the sodium polonide Na2Po compound have been studied through the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) and tight-binding linear muffin-tin orbital (TB-LMTO) methods. The exchange–correlation potential was treated within the local density approximation for the TB-LMTO calculations and within the generalized gradient approximation for the FP-LAPW + lo calculations. In addition, Tran and Blaha-modified Becke–Johnson (TB-mBJ) potential and Engel–Vosko generalized gradient approximation were used for the electronic and optical properties. Ground state properties such as the equilibrium lattice constant, bulk modulus and its pressure derivative were calculated and compared with available data. The single-crystal and polycrystalline elastic constants of the considered compound were calculated via the total energy versus strain in the framework of the FP-LAPW + lo approach. The calculated electronic structure reveals that Na2Po is a direct band gap semiconductor. The frequency-dependent dielectric function, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for a wide energy range. The variations of the lattice constant, bulk modulus, heat capacity, volume expansion coefficient and Debye temperature with temperature and pressure were calculated successfully using the FP-LAPW + lo method in combination with the quasi-harmonic Debye model.

Composition dependence of the optical properties and band structure of the zinc-blende ZnS1-xOx: a first principles study

We present first principles calculations of structural, electronic and optical properties of ZnS1−xOx in the zinc-blende phase. We employ the full potential linearized augmented plane wave method within the density functional theory in the generalized gradient approximation and Engel–Vosko generalized gradient approximation. Features such as the lattice constant, the bulk modulus and its pressure derivative are reported. The agreement between our calculated results and available experimental and theoretical data is generally good. Direct and indirect energy band gaps as a function of the oxygen composition in the material of interest are presented and discussed. The material under investigation is found to remain a direct band gap semiconductor over all the alloy composition range (0–1). Furthermore, the optical properties such as the dielectric function, the refractive index, the reflectivity and the electron loss energy have also been reported and analysed.

First principles study of three dimensional topological phases of GdxY1−xPtBi (x=0, 0.25, 0.5, 0.75, 1) alloys

The structural, electronic and magnetic properties and existence of topological phase of GdxY1−xPtBi (x=0, 0.25, 0.5, 0.75, 1) alloys are studied using density functional theory. The lattice constant and bulk modulus of these alloys in ferromagnetic phase are calculated using the generalized gradient approximation (GGA) in the presence of spin-orbit coupling. To investigate the electronic properties and existence of topological phase, the local density approximation (LDA), GGA and Engel–Vosko generalized gradient approximation (EV-GGA) are used. The electron density of states, band structure and topological band order of these alloys are investigated. Furthermore the variations of magnetic momentum, the linear coefficient of electronic specific heat and the band inversion strength with increase of x are investigated.

Electronic structure of alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr3Be3B3O9F4 single crystal: DFT approach

The electronic band structure, total and angular momentum resolved projected density of states for NaSr3Be3B3O9F4 are calculated using the all-electron full potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method. The calculations are performed within four exchange correlations namely; local density approximation (LDA), general gradient approximation (PBE-GGA), Engel–Vosko generalized gradient approximation (EVGGA) and the recently modified Becke–Johnson potential (mBJ). Calculations suggest that NaSr3Be3B3O9F4 is a direct wide band gap semiconductor. The exchange correlations potentials exhibit significant influence on the value of the energy gap being about 4.82eV (LDA), 5.16eV (GGA), 6.20 (EVGGA) and 7.20eV (mBJ). The mBJ approach succeed by large amount in bringing the calculated energy gap closer to the experimental one (7.28eV). The angular momentum resolved projected density of states shows the existence of a strong hybridization between the various orbitals. In additional we have calculated the electronic charge density distribution in two crystallographic planes namely (101) and (00−1) to visualized the chemical bonding characters.

Chalcogenides-based quantum dots: Optical investigation using first-principles calculations

The full potential-linearized augmented plane wave (FP-LAPW) method is implemented in WIEN2K code to calculate the indirect energy gap (Γ–X) using density functional theory (DFT). The Engel–Vosko generalized gradient approximation (EV-GGA) and modified Becke Johnson (mBJ) formalisms are used to optimize the corresponding potential for energetic transition and optical properties calculations of lead chalcogenides (PbS1−xTex) alloys as a function of quantum dot diameter and is used to test the validity of our model of quantum dot potential. The refractive index and optical dielectric constant are investigated to explore best applications for solar cells.