Generalized Gradient Approximation GGA Research Articles

First‐Principles Study of the Influences of Point Vacancies (VGa, Hi) on the Photocatalytic and Magnetic Performance of Ga2O3:Li/Na/K Systems

Under vacuum environment, an H interstitial must exist when Ga2O3 is prepared by organometallic chemical vapor deposition. However, few first‐principles systematic studies have been conducted on the influences of point vacancies (VGa, Hi) on the photocatalytic performance and magnetism of Ga2O3:(Li or Na or K) systems, and VGa is a challenge in experiments. Therefore, the first‐principles generalized gradient approximation GGA + U theory is adopted in this study. A first‐principles study is conducted on the formation energy (E f), photocatalytic performance, and magnetism of Ga30MO48 (M = Li or Na or K) and Ga30MHiO48 systems. In the results, it is shown that under Ga‐poor conditions, the Ga30MO48 and Ga30MHiO48 systems are structurally stable and prone to doping. The Ga30MHiO48 system has lower E f, more structural stability, and easier doping than the Ga30MO48 system. The Ga30KO48 system exhibits magnetism, mainly generated by the O1−‐2p spin‐polarized wandering electrons near VGa. The spin‐polarized O2−‐2p and Ga‐4s states near VGa contribute to the hybrid coupling double‐exchange interaction. Moreover, the visible spectrum of the Ga30LiHiO48 system exhibits a significant redshift, a relatively high carrier activity, carrier separation, and relative maximum lifetime. It is relatively best as a photocatalyst.

Determination of Band Structure and Compton profiles for Aluminum-Arsenide Using Density Functional Theory

First-principles computations of the electrical characteristics of AlAs have been carried out using the density functional theory-DFT and the Local Density Approximation-LDA,methods (DFT) and Generalized Gradient Approximation-GGA. We utilized the CASTEP's plane wave basis set implementation for the total energy computation (originally from Cambridge Serial Total Energy Package). We used to look at the AlAs structure's structural parameter. The band gap was overestimated by the Generalized Gradient Approximation and LDA techniques, although the band gap predicted by the GGA is more in line with the experimental finding, according to the electronic structure calculation utilizing the two approximations. A semiconductor with a straight band-gap of 2.5 eV is revealed by the GGA calculation. The energy band diagram is used to calculate the total and partial densities of AlAs states. Multiple configurations of the ionic model were calculated. of Al+xAs−x (0.0 ≤ x ≤ 1) are also performed utilizing free-atom profiles. According to the ionic model, 0.75 electrons would be transferred from the valence 5p state of aluminum to the 3p state of Arsenide.

Structural, electronic and thermoelectric properties of PbS, PbSe and their ternary alloy PbSe1−xSx

Solid-state thermoelectric devices offer the possibility of exploiting waste heat from engines and power plants and converting it into electrical energy. One of the greatest challenges in the development of thermoelectric material systems is to find new thermoelectric materials with high thermoelectric figures of merit ZT. In this work, the structural, electronic and thermoelectric properties of PbSe[Formula: see text]S[Formula: see text] ([Formula: see text], 0.25, 0.50, 0.75 and 1) semiconductors are investigated by applying density functional theory in a full potential linearized augmented plane wave method (FP-LAPW). Calculations of structural properties were completed using the generalized gradient approximation GGA of Perdew Burke and Ernzerhof PBE to get reliable lattice constant results with experimental values. The obtained electronic results show that the PbSe[Formula: see text]S[Formula: see text] material is a narrow band gap semiconductor. In addition, the thermoelectric properties are studied on the basis of the fully iterative solution of the Boltzmann transport equation. PbSe[Formula: see text]S[Formula: see text] had a high figure of merit indicating that our materials are promising candidates in thermoelectric applications.

A DFT study of new full Heusler compound Li2MgC insights into the structural, electronic and thermoelectric properties: A high efficiency performance thermoelectric material

Structural, electronic and thermoelectric properties for full Heusler compound Li2MgC were studied using the full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT), implemented in the Wien2k package. The term of the exchange and correlation potential (XC) is treated by the generalized gradient approximation GGA and Trans-Blaha-modified Becke–Johnson (mBJ-GGA). From the various calculations, it emerges that the Cu2MnAl type structure is more suitable for this compound than that of the Hg2CuTi type structure; moreover, this compound is stable in the non-magnetic (NM) state. Furthermore, this compound exhibits a semi -conductor behavior with an indirect band gap at Γ-X direction. The calculated formation and cohesion energies are negative, which clearly and unequivocally indicates the thermodynamic stability of the compound studied and that it can be synthesized experimentally. Otherwise, this compound is characterized by a high figure of merit (ZT) (close to unity), making it a promising candidate for thermoelectric applications.

Theoretical investigation of the physical properties of cubic perovskite oxides Sr[formula omitted] ([formula omitted] Sc, Ge, Si)

Various physical properties (electronic, optical and thermoelectric) of cubic perovskite oxides SrXO3 (X= Sc, Ge, Si) are investigated by using the density functional theory (DFT) within Wien2K code. This code is based on different approximations such as generalized gradient approximation GGA, PBEsol, LDA, WC and the modified Becke–Johnson exchange potentials (mBJ, nmBJ and unmBJ). Structural properties and the optimization have been calculated using PBEsol functional which showed a significant results that are in good agreement with the experimental ones. The results for physical properties such as electronic, thermoelectric and optical are analyzed in detail by using the nmBJ approximation. The obtained results present an opening gap for SrSiO3, SrGeO3 and a metallic behavior for SrScO3. An average of transmittance which is about 94% to 97% was observed in the range of visible light. The increase of electrical conductivity with temperature confirms the effect of thermal agitation on the concentration of charges carriers using BolzTrap2 Package. Lastly a phonon dispersion was made and show that for X= Ge and Si, the structure is relatively stable while SrScO3 is dynamically unstable. These results prove the ability that these materials can be exploited in many applications and manufacturing of optoelectronics for Sensors.

DFT Investigations on Structural Stability and Ferromagnetism in V-Doped MgTe for Spintronic Applications

Based on the first-principle calculations using the KKR-CPA method with the generalized gradient approximation GGA, we study the doping effect of the transition element Vanadium on the structural, electronic and magnetic properties of Magnesium Telluride MgTe. The calculations show that pure MgTe is an intrinsic non-magnetic semiconductor with a direct energy bandgap of 1.75 eV. The introduction of Vanadium impurities renders the doped compound half-metallic with a spin polarization equal to 100% at the Fermi level. Furthermore, the ferromagnetic phase is the most stable one for a concentration The double exchange interaction is the mechanism responsible for magnetism in MgTe. The total magnetic moment of the doped system varies from 0.354 μB to 0.712 μB for concentrations of 12% to 25% respectively, while the critical temperature increases from 124 K to 700 K for the same concentration values. Therefore, material can be suitable for spintronic applications.

First principle investigation of physical properties of MNiBi: (M = Sc, Y) half-Heusler compounds

We have investigated the half Heusler compounds MNiBi (M=Sc, Y), using the framework of density functional theory DFT within the full potential linearized augmented plane wave (FP-LAPW) method and studied the structural, electronic, optical and elastic properties. The structural properties are predicted using the Generalized Gradient Approximation GGA and Local Density Approximation LDA, the calculations reveal that Lattice constants and other structural parameter are better matched in GGA approximation with experimental and theoretical result than LDA approximation. The calculated band structure and the density of states (DOS) with GGA, LDA and Tran and Blaha modified Becke-Johnson (TB-mBJ) exchange-correlation potentials, indicates a semiconducting nature with indirect narrow band gaps for both compounds ScNiBi and YNiBi, it shown from result that using (TB-mBJ) functionals is much more successful than the LDA and GGA approach in estimating bandgaps for our half Heusler ScNiBi and YNiBi. Optical properties of the compounds under investigation are also reported in this paper, high absorptivity are observed in the visible and ultraviolet region. The bulk modulus, shear modulus, young’s modulus, and other elastic constants are computed to discuss their elastic properties.

First‐Principles Calculations of Physical Properties and Stability of Orthorhombic FeN2 under High Pressure

The physical properties and stability of orthorhombic FeN2 under high pressure remain an open question. The spin‐polarized first‐principles calculations within the generalized gradient approximation GGA + U functional are used to study the structural, elastic, electronic, magnetic properties and the stability of orthorhombic FeN2 under high pressure. The variations of the lattice constants and bond lengths as a function of pressure in the range 0–100 GPa are presented. The elastic constants, moduli, Poisson's ratio, elastic wave velocities, Debye temperature, and thermal expansion coefficient as a function of pressure in the range 0–100 GPa are also given. The high bulk modulus and low compression make it a promising high‐energy‐density material. FeN2 is both mechanically and dynamically stable in the studied pressure range. FeN2 is elastic anisotropic and its anisotropy increases with pressure. At pressure less than 45 GPa, the orthorhombic FeN2 is a magnetic metal, while at pressure increasing to 45 GPa, a nonmagnetic metal is obtained. When the pressure goes beyond 45 GPa, the outline of the density of states is similar, showing that the pressure has less effect on electronic properties. It is hoped that these results can provide reference for further researches.

Effects of Doping Cadmium Atoms on the Electronic and Optical Properties of (n, 0) Zigzag SWCNTs: DFT Approach

Effects of doping cadmium atoms on the electronic and optical properties of (n, 0) zigzag single-wall carbon nanotubes SWCNTs are investigated by density functional theory DFT, using ultrasoft pseudopotential generalized gradient approximation GGA approach. The electronic and optical properties of the zigzag SWCNTs are susceptible and dependent on the n index and diameter of the tube; these features have only in nanotubes. Adding any impurity to the Zigzag SWCNTs must be caused to change in properties. The density of states for Cd-doped and un-doped SWCNTs increases with an increase in n index because of overlap valence and conduction bands in all situations (small bandgap). All samples have metallic characteristics. Almost all absorption and reflectivity spectra peaks are produced in the UV range. It can be noted that the peaks of the un-doped samples are higher than that of Cd-doped. Consequently, the material’s ability to store energy and photon absorption for un-doped nanotubes is larger than Cd-doped zigzag SWCNTs. These results are achieved in the figures of dielectric functions.

Ab-initio and Monte Carlo Simulations of the New Half-Heusler Alloy NiCrGa

Abstract: In this work, we are investigating the electronic and magnetic properties of the new NiCrGa half-Heusler alloy (HHA), by using the ab-initio and Monte Carlo simulations (MCSs). The ab-initio method is performed under the pseudo-potential method and the generalized gradient approximation GGA. The density of states (DOS) and the band structure calculations show that the alloy NiCrGa reveals a nearly half-metallic (HM) behavior. In particular, the Slater-Pauling (SP) rule has been confirmed when using the magnetic moments of the individual constituents of the NiCrGa compound. The Monte Carlo simulations (MCSs) are accomplished using the Metropolis algorithm. In order to determine the transition temperature, we are based on the behavior of the total magnetization and susceptibility of this material. We also presented and discussed the hysteresis loops of the half-Heusler compound, for fixed values of temperature, exchange coupling interactions and crystal field. It is found that when increasing the crystal field, the surface of the loops increases and vice versa. Keywords: Half-Heusler alloy, NiCrGa, Slater pauling, DFT method, Monte Carlo study.

Ferromagnetic Half-Metal for Spintronic Applications: Ab-Initio Calculation

Abstract The density functional theory (DFT) is used to study the structural, electronic, magnetic properties of Heusler Alloy compounds PdCoMnAl. The calculations are performed via FP-LAPW computational approaches as part of the generalized gradient approximation GGA and modified Becke–Johnson TB-mBJ for exchange-correlation potential. The prediction of the structure of the energy bands and of the densities of states shows a strong hybridization between the states d of the atoms of the transition metals of high valence (Pd) and the states d of the atoms of the transition metal of low valence (Mn) and (Co), which generates a half-metallic gap. In addition, the densities of total and partial states (PDOS) and the results of magnetic spin moments reveal that this compound is stable and ideal half-metallic ferromagnetic. The effects of the unit cell volume on the half-metallic and magnetic properties are crucial. It is interesting to note that our results of the total magnetic moment for PdCoMnAl equal to 5 µB per unit cell, nicely follow the rule µtot = Zt-18.

Magnetic properties and half metallic behavior of the Full-Heusler Co2FeGe alloy: DFT and Monte Carlo studies

The study of structural, electronic and magnetic alloy properties of the full-Heusler Co2FeGe has been undertaken using the first principle method based on the density functional theory (DFT). In this work, we have predicted and underlined the mechanism of the half-metallic behavior of the full-Heusler Co2FeGe alloys by using the Monte Carlo simulations. We have used the full potential linear augmented plane wave (FPLAPW) method as implemented in the Wien2K code to forecast the electronic and magnetic properties of the studied system. We have used the generalized gradient approximation GGA for the treatment of exchange energy and correlation. We have also taken into account the strong correlations orbital of Co and Fe atoms by applying the GGA ​+ ​U approximation founded on DFT ​+ ​U. The GGA ​+ ​U gives a good result showing that compound Co2FeGe is a half-metallic ferromagnetic (HMF) through a large gap of 1.20 ​eV. The value of the magnetic moment is used as input to calculate the magnetic parameter of this alloy when using the Monte Carlo simulations. By the help of the proposed model the temperature dependency of the magnetization, the susceptibility and the specific heat, is studied. The phase transition is of second order type at the critical temperature point. This temperature is in good agreement with the available experimental data.

Cu2XSnS4 (X = Mn, Fe, Co) semiconductors: Boltzmann theory and DFT investigations

Cu2XSnS4 (X = Mn, Fe, Co) semiconductor represent one of the most promising quaternary family for the photovoltaic devices. For this purpose, a comparative study of structural, electronic, linear/non-linear optical and thermoelectrical properties of Cu2XSnS4 based on the first-principles calculations and Boltzmann theory was done, using the generalized gradient approximation GGA with applying the Hubbard on-site coulombic correction to Mn, Fe and Co cations. The computation of the lattice constants shows a good agreement with the experimental results, also the simulation of X-ray diffraction (XRD) spectra shows that the compounds have crystallized in the polycrystalline kesterite form with a preferential orientation along (112) plane. The GGA + U method offering that CMTS, CFTS and CCTS materials exhibit a duality ferromagnetic semiconductor behavior. The optical properties showed good optical absorption in order of 20 and 30 (104 cm−1) for the three compounds, and a high optical conductivity in the visible range. Thus, the non-linear optical properties as well as suitable optical band gaps of about 1.44–1.56 eV confirms the applicability of CMTS, CFTS and CCTS materials as absorbent layers in photovoltaic solar cells. In addition, the thermoelectric properties such as electrical conductivity (σ/τ), Seebeck coefficient (S) and power factor (S2σ/τ) as a function of temperature were investigated using Boltztrap package, we have found that CMTS, CFTS and CCTS kesterite materials exhibit p-type behavior and good thermoelectric transport properties in the temperature range of 300 - 800K, therefore, we expect these materials to be potential candidates for clean energy applications.

A potential full Heusler thermoelectric material CO2ZrZ (Z=Al, Si, Ga and Sn) in low temperature: An Ab-initio investigation

The structural, electronic, magnetic, elastic and thermoelectric properties of full-Heusler alloys Co2ZrZ (Z = Al, Si, Ga and Sn) are investigated using the augmented plane wave method (FP-LAPW) based on the framework of spin density functional theory. The term of the exchange and correlation potential (XC), is treated by the generalized gradient approximation GGA and Trans-Blaha-modified Becke–Johnson (TB-mBJ). The results obtained showed that the Cu2MnAl-type structure has more stable energy than the Hg2CuTi-type structure for all the full-Heusler studied. From electronic calculations, it is found that all the compounds studied have an indirect band gap with a half-metallic behavior. Furthermore, we also found that all materials have integral magnetic moments which are mainly due to 100% spin polarization at Fermi energy. The calculated elastic constants and the anisotropy shear factors indicate that these compounds have a ductile character and are mechanically stable. Finally, we calculated the thermoelectric properties by applying Boltzmann theory as implemented in the BoltzTraP code. The results obtained for the merit factor (ZT) and Seebeck coefficient (S) make these materials promising candidates in thermoelectric applications and in spintronics devices.

Full Heusler alloys, with high absorption coefficient, insight into the optical properties of Li2CaC and Li2SrC

Structural, electronic, elastic and optical properties of full Heusler compounds Li2CaC and Li2SrC were studied; using the full potential linearized augmented plane wave method based on the density functional theory, implemented in the Wien2k package. The exchange and correlation potential is treated by the generalized gradient approximation GGA and Trans-Blaha-modified Becke–Johnson. We have found that the structure of Cu2MnAl-type has more stable energy than the one of Hg2CuTi-type for both compounds studied. These compounds have semiconductor behaviour with a direct band gap at Γ-Γ direction with values of 1.127 eV and 0.979 eV for Li2CaC and Li2SrC respectively. The calculated formation and cohesive energies are all negative, which exhibit that these alloys have a good chemical stability. The optical properties shows a high absorption coefficient,which gradually increases from 7 × 104cm−1 to 39 × 104cm−1 through the visible domain of light, and the high reflectivity which exceeds 30% in the visible domain of light for both compounds, allowing the useful of these full Heusler materials in optoelectronic applications, including solar and photovoltaic cells. Although, no available theoretical or experimental results for these compounds to compare it with our findings. We hope that this study can pave the way for experimental or theoretical research in the future.

Ferromagnetic alloy for high-efficiency photovoltaic conversion in solar cells: first-principles insights when doping SnO2 rutile with coupled Eu-Gd.

From results of first-principles all-electron full-potential augmented spherical-wave calculations within a generalized gradient approximation, a materials design for half-metallic ferromagnetic semiconductors based on (Eu,Gd)-doped SnO2 rutile is proposed. Moreover, their half-metallic ferromagnetic properties are homogenous and energetically stable for different crystallographic directions. Therefore, the interatomic exchange interaction between the spins of double impurity ions is a long-range ferromagnetic interaction that is sharply weakened when the distance between Eu–Gd increases. The double impurities most likely substitute adjacent Sn sites and result in strong ferromagnetic interactions by p–f hybridization between rare earth 4f and Op states. There is great interest in the configuration that has the lowest energy difference, where the double impurity substitutes the nearest neighbor Sn sites along the z-axis of SnO2 rutile. Generalized gradient approximation GGA and GGA+U calculations were performed. According to our revPBE-GGA calculations, the ferromagnetic compound is capable of absorbing 96% from the visible light. Furthermore, the transport properties at room temperature ensure excellent electrical conductivity, low thermal conductivity, and the most optimal figure of merit (ZT), which leads to high thermoelectric performance. As the latter are closely related to free flow charge carriers, we can subsequently predict that the ferromagnetic alloy will be able to be a great power source for highly effective photovoltaic conversion in solar cells. Further experimentation will be necessary to obtain confirmation of our ab initio predictions.

Spinelectronic investigation of the quaternary vanadium fluoride Rb2NaVF6: Ab-initio method

In this study, we have investigated the structural, electronic, and magnetic properties of the Rb2NaVF6 compound. We have performed our calculations by the use of first-principle methods based on spin-polarized density functional theory, where the electronic exchange-correlation potential is treated by the generalized gradient approximation GGA- PBEsol coupled with the improved TB-mBJ approach. The calculated structural parameters of Rb2NaVF6 are in good agreement with the available experimental data. Rb2NaVF6 exhibits a half-metallic ferromagnetic feature with a spin polarization of 100 % at the Fermi level and a direct large half-metallic gap of 3.582 eV. The total magnetic moments are 2 μB. This material is half-metallic ferromagnets, and it can be potential candidates for spintronics applications at a higher temperature.

First-principles study on electronic, magnetic properties and optical absorption of vanadium doped rutile TiO2

The electronic, magnetic properties and optical absorption of vanadium (V) doped rutile TiO2 have been studied by the generalized gradient approximation GGA and GGA+U (Hubbard coefficient) approach respectively. On the one hand, we consider the influence of vanadium with different doping concentration on the electronic structure. On the other hand, we study double V atoms doped TiO2, mainly study four V-doped TiO2 configurations, and find the magnetic ground states are ferromagnetic state. For the TiO2@V-V1, TiO2@V-V3 and TiO2@V-V4 configurations without O ion as bridge between V-V atoms, there will have a metastable state of antiferromagnetic configurations, while, for the TiO2@V-V2 configurations with an O ion as bridge between V-V atoms, due to the existence of superexchange between V-O-V, there will only exist the ground state of ferromagnetic state and there are no other metastable configurations. Furthermore, the optical properties of V-doped TiO2 are calculated. The results show that the V-doped TiO2 has strong infrared light absorption and visible light absorption.

Structural, electronic, and optical properties of AlNxSb1−x alloys through TB–mBJ–PBEsol: DFT study

The objective of this paper is the examination of structural, electronic, and optical properties of binary AlSb, AlN, and their novel ternary AlNxSb1−x alloys (x = 0.25, 0.5, and 0.75), within the full-potential linearized augmented plane wave method based on the density functional theory as implemented in the WIEN2K code. The computed negative formation energies of AlNxSb1−x alloys prove that these compounds are thermodynamically stable. The structural parameters are calculated using the generalized gradient approximation GGA–PBEsol, such as the lattice parameters, bulk modulus, and pressure derivatives, which are in good accordance with both theoretical and experimental data for binary compounds. However, for the ternary alloys, our results are considered as a first prediction. The lattice constants and the bulk modulus are compared with Vegard’s law and the linear concentration dependence. The Tran–Blaha-modified Becke–Johnson approach “TB–mBJ” is employed to determine the electronic and optical properties; the results demonstrate that the binary compounds have indirect band gaps (Γ–X), whereas the ternary AlNxSb1−x alloys exhibit direct band gaps (Γ–Γ) semiconductors, with values of 0.472, 0.915, and 1.962 eV for AlN0.25Sb0.75, AlN0.5Sb0.5, and AlN0.75Sb0.25, respectively. The obtained results are reported, discussed, and compared with previous and the experimental data.

Robust half metallicity state with the hydrostatic and tetragonal distortion for a new quaternary Heusler ZrTiRhGa: FP-LAPW calculations

The structural, mechanical, electronic and magnetic properties of quaternary Heusler ZrTiRhGa alloy have been investigated by using the first-principles calculations within the generalized gradient approximation GGA. The results of our calculations show that the type (I) of ZrTiRhGa, with the ferromagnetic (FM) state, is the most stable configuration among three possible configurations. The GGA + U calculations, where U is on-site Coulomb interaction correction, are performed to investigate the relationship between band gap and Hubbard potential.The calculated results showed that ZrTiRhGa compound is half-metallic material (HMM) with complete spin polarization around the Fermi level. The total magnetic moment is 2 μB per formula unit and follows the Slater-Pauling rule μt = Zt−18. The calculated elastic constants, cohesive and formation energy, for ZrTiRhGa compound, were analyzed in detail and reveal the mechanical stability. In addition, we investigated the sensitivity of the half-metallicity with two structural-type changes: hydrostatic and tetragonal deformation. Our calculations show that the half-metallicity can be preserved with lattice constants from 5.74 Å to 7.12 Å, under the influence of hydrostatic strain and in the range of the c/a ratio from −8% to 12% with the effect of the tetragonal strain. For ZrTiRhGa, since there is no available experimental data, our calculations are considered as first predictions.