Generalized Gradient Approximation Scheme Research Articles

Optical and thermal properties of Scanduim chalcogenides: DFT study

The full potential linearized augmented plane wave (FP-LAPW) calculations based on
 density functional theory (DFT) is performed to study the structural, electronic, optical
 and thermodynamic properties of Scanduim chalcogenides ScX (X = S, Se, Te) and them
 ternary alloys at equilibrium as well as under pressure. The revised Perdew-Burke-Ernzerhof generalized gradient approximation (GGA) is used to calculate the structural properties. The electronic and optical properties are calculated employing the GGA and the modified Becke-Johnson (mBJ) approaches. Moreover, the calculated lattice parameters agree well with the experiment results. The NaCl structure (B1) of the scandium chalcogenides undergo under pressure a structural phase transition to CsCl-type (B2) and ZnS-type (B3). The binary and ternary alloys indicate a metallic behavior using GGA and mBJ scheme. The interband contribution to the optical properties is investigated and the parameters ε1(ω), ε2(ω) and n(ω) are calculated. A Quasi-harmonic Debye model is applied to calculate the thermal properties.

Structural, electronic, magnetic, elastic and thermodynamic properties of Ni 4 N anti-perovskite

ABSTRACT We have analyzed the structural, electronic, magnetic, elastic and phonon properties of anti-perovskite by using density functional theory (DFT) based on the generalized gradient approximation scheme and Monte Carlo simulations within the Ising model. The structural investigation exposes the ferromagnetic configuration stability of the compound. Also, the density of states (DOS) and band structure calculations show a metallic behavior of . The investigated elastic constants, phonon dispersion and density phonon states showed that the compound is mechanically and dynamically stable. We also found that the is ductile from the Poisson's ratio, Pugh's ratio and Cauchy pressure. The thermodynamic parameters like heat capacity, Debye and melting temperature have also been calculated. The critical exponents of obtained by Monte Carlo simulation are highly in agreement with the 3D-Ising model around the critical temperature . The obtained value of agrees reasonably well with available experimental and theoretical works.

Isosymmetric compression of cubic halide perovskites mathrm{ABX}_{3} (A=K, Rb, Cs; B=Ge, Sn, Pb and X=Cl,Br,I)-influence of cation\u2013anion exchange: a first principle study

Halide perovskites are potential candidates for their use in solar cells. In this study, an investigation of the structural, mechanical and electro-optical properties of mathrm{ABX}_{3} (A=K, Rb, Cs; B=Ge, Sn, Pb and X=Cl,Br,I), under isosymmetric compression, is presented. All the calculations are performed with generalized gradient approximation schemes. We have examined the effect of cation and anion substitution on their overall properties.

Correlation effect on the electronic structure of RECo2 (RE= Gd and Eu) intermetallic compounds: A comparative study

This work reports an ab initio study of the electronic and magnetic properties of the binary phases Laves GdCo2 and EuCo2 of MgCu2 type. The linearized augmented plane wave method with total potential was used (FP-LAPW). To estimate the exchange and correlation potential, we introduced the generalized gradient approximation (GGA) and GGA + U (with a Hubbard “U” parameter) to take into account the correlation effects. The results show that the obtained magnetic moments corroborate the data found in literature as well. Note that the GGA + U gave magnetic moments greater than those calculated using the GGA scheme. To obtain further insight into the type of states associated with each orbital, the projected densities of states of the 4f-Gd, 4f-Eu and 3d-Co orbitals were also calculated using GGA and GGA + U respectively, to obtain additional information on the electronic and magnetic properties of these compounds. This work highlights the role of the correlated electrons processing for an accurate description of these binary Laves phases compounds.

Calculations of the structural and optoelectronic properties of cubic CdxZn1−xSeyTe1−y semiconductor quaternary alloys using the DFT-based FP-LAPW approach

The structural and optoelectronic properties of technologically important CdxZn1−xSeyTe1−y quaternary alloys have been calculated using the density functional theory (DFT)-based full potential (FP)-linearized augmented plane wave (LAPW) approach. The exchange–correlation potentials are calculated using the Perdew–Burke–Ernzerhof (PBE)-generalized gradient approximation (GGA) scheme for the structural properties and both the modified Becke–Johnson (mBJ) and Engel–Vosko (EV)-GGA schemes for the optoelectronic properties. A direct bandgap ($$ \varGamma $$–$$ \varGamma $$) is observed for all the examined compositions in the CdxZn1−xSeyTe1−y quaternary system. At each cationic (Cd) concentration x, the lattice constant decreases while the bulk modulus and bandgap increase nonlinearly with increasing anionic (Se) concentration y. On the other hand, a nonlinear increase in the lattice constant but a decrease in the bulk modulus and bandgap are observed with increasing cationic concentration x at each anionic concentration y. The contour maps calculated for the lattice constant and energy bandgap will be useful for designing new quaternary alloys with desired optoelectronic properties. Several interesting features are observed based on the study of the optical properties of the alloys. The compositional dependence of each calculated zero-frequency limit shows the opposite trend, while each calculated critical point shows a similar trend, with respect to that found for the compositional dependence of the bandgap. Finally, the results of these calculations suggest that ZnTe, InAs, GaSb, and InP are suitable substrates for the growth of several zincblende CdxZn1−xSeyTe1−y quaternary alloys.

Half-metallicity and magnetism of CoFeHfGe novel quaternary Heusler alloy in bulk form as well as (100) and (001) surfaces: An ab initio study

In this study, we investigated the electronic and magnetic nature of the LiMgPdSn-type CoFeHfGe quaternary Heusler alloy in the bulk form as well as the (100) and (001) surfaces using density functional theory within the generalized gradient approximation scheme. The bulk CoFeHfGe alloy was predicted to exhibit half-metallic behavior with an electronic band gap of 0.37 eV and 100% spin-polarization at an equilibrium lattice parameter of 6.08 Å. The elastic constants and phonon dispersion confirmed the mechanical and dynamical stability of the bulk form considered. The total magnetic moment was determined as 1μB/f.u. for the CoFeHfGe alloy. The atomic relaxation and surface energy were investigated for the (100) and (001) surfaces of the CoFeHfGe alloy, and the results indicated that the slabs are stable, where CoFe (001) has the lowest surface energy among all of the terminations. For (100) and (001) slabs of the CoFeHfGe alloy, we found that the half-metallicity is destroyed due to the surface states and the HfGe (100) slab has the highest spin polarization of 90.72%, and thus it can be used in giant magnetoresistance devices. The magnetic moments in the layers of the HfGe (100) slabs are similar to the corresponding bulk and magnetic moments of the surface atoms, where they tend to increase with depth in the CoFe (100) slab.

Half-Metallic Property Induced by Double Exchange Interaction in the Double Perovskite Bi2BB'O6 (B, B' = 3d Transitional Metal) via First-Principles Calculations.

In this paper, we identify three possible candidate series of half-metals (HM) from Bi-based double perovskites Bi2BB′O6 (BB′ = transition metal ions) through calculations utilizing the density functional theory (DFT) and full-structural optimization, in which the generalized gradient approximation (GGA) and the strong correlation effect (GGA + U) are considered. After observing the candidate materials under four types of magnetic states, i.e., ferromagnetic (FM), ferrimagnetic (FiM), antiferromagnetic (AF), and nonmagnetic (NM), we found eight promising candidates for half-metallic materials. Under the GGA scheme, there are three ferromagnetic-half-metal (FM-HM) materials, Bi2CrCoO6, Bi2CrNiO6 and Bi2FeNiO6, and three FiM-HM materials, Bi2FeZnO6, Bi2CrZnO6 and Bi2CoZnO6. With implementation of the Coulomb interaction correction (GGA + U), we find two stable half-metallic materials: Bi2CrNiO6 and Bi2CrZnO6. We determine that the stability of some of these materials are tied to the double exchange interaction, an indirect interaction within the higher powers of localized spin interaction among transition metals via oxygen ions. Found in half-metallic materials, and especially those in the ferromagnetic (FM) state, the double exchange interaction is recognized in the FM-HM materials Bi2CrCoO6 and Bi2FeNiO6.

Investigation of half-metallicity and magnetism of bulk and (111)-surfaces of Fe2MnP full Heusler alloy

The structural, electronic, magnetic, elastic and phonon properties of bulk and electronic and magnetic properties of (111)-surfaces of AlCu2Mn-type Fe2MnP Heusler alloy have been investigated by using density functional theory based on the generalized gradient approximation scheme. The cohesive energy confirmed the stability of the alloy considered at an equilibrium lattice constant of 5.5628 Å. We observed a half-metallic nature in the bulk alloy with energy band gaps of 0.34 eV and spin-flip gaps of 0.09 eV with 100% spin-polarization in the minority spin electrons. The computed magnetic moments for the Fe2MnP alloy are found to be 4 μB/f.u. The investigated elastic constants, phonon dispersion and density phonon states showed that the Fe2MnP alloy is mechanically and dynamically stable. We also found that the alloy is ductile from the Poisson's and B/G ratios. The half-metallic ferromagnetic nature is preserved in the P (111)-terminated slab among all terminations with 100% spin-polarization which is a crucial property of spin devices, since it can be optimize their performance. The spin-polarization clearly decreases by nearly 75% for Fe (111) and Mn (111)-terminated slabs due to surface states located below the Fermi level. Moreover, the computed atomic magnetic moments of (111)-slabs of the Fe2MnP Heusler alloy are extremely close to the atomic bulk values.

Fundamental properties of scandium chalcogenides and their alloys: DFT study

The full-potential linearized-augmented plane wave calculations based on density functional theory are performed to study the structural, electronic, optical and thermodynamic properties of scandium chalcogenides ScX (X = S, Se, Te) and their ternary alloys at equilibrium as well as under pressure. The revised Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) is used to calculate the structural properties. The electronic and optical properties are calculated employing the GGA and the modified Becke–Johnson (mBJ) approaches. Moreover, the calculated lattice parameters agree well with the experiment results. The structure NaCl-type (B1) of the scandium chalcogenides undergoes under pressure a structural phase transition to CsCl-type (B2) and ZnS-type (B3). The binary and ternary alloys indicate a metallic behavior using GGA and mBJ scheme. The interband contribution to the optical properties is investigated by calculating the dielectric parameters e1(ω), e2(ω) and the index of refraction n(ω). A quasi-harmonic Debye model is applied to calculate the thermal properties.

A DFT study of the electronic and magnetic properties of Cu2Cr1−xVxGa alloys

We have investigated the electronic and magnetic properties of the doped Heusler alloys Cu2Cr[Formula: see text]V[Formula: see text]Ga ([Formula: see text], 0.5, and 1) using first-principles density functional theory within the generalized gradient approximation scheme. Lattice constants of all phases were determined, and the absence of energy gap in both the spin channels predicts that the materials are metallic. The calculated formation energies are negative, indicating stability of these compounds. Electronic structure and magnetic behavior are reported for the first time for the Cu2Cr[Formula: see text]V[Formula: see text]Ga alloy. It was found that the alloys are ferromagnetic, and metallic witch is confirmed by GGA[Formula: see text]U calculation.

DFT based structural, electronic and optical properties of [formula omitted] compounds: PBE-GGA vs. mBJ-approaches

The ground state structural, electronic and optical properties of B1-XInXP (X = 0.0, 0.25, 0.5, 0.75, 1.0) phases have been scrutinized with zinc-blend structure. The full potential linear augmented plane wave method is applied in the framework of density functional theory employing wien2k package. The electronic structure calculations are treated with superior modified-Becke-Johnson potential along with Perdew-Burke-Ernzerhof generalized gradient approximation scheme to harvest the precise energy band gaps in order to get close to experimental outcomes. The computations on ground state structural properties such as volume optimization, equilibrium lattice constants, total equilibrium energy, bulk modulus, compressibility and electronic properties density of states, band structure, energy band gap and in optical properties such as dielectric constant, absorption coefficient, refractive index, electron energy loss function, sum rule, optical reflectivity have been established. The calculated structural, electronic and optical parameters are in excellent agreement with (if) previously reported theoretical and experimental work. The comparative study entailed that mBJ-approach is in strong recommendation for the band gap treatment of materials as it investigates the most close comparable outcomes with the experimental results.

Search for new d0 half-metallic materials: theoretical investigation on KCaC[formula omitted]Six (x = 0; 0.25; 0.5; 0.75 and 1) compounds

In recent years, the investigations on d0 half-metallic materials have become the new trend in the search of novel materials for applications in spintronic devices. In this work, the structural, electronic and magnetic properties of KCaC1−xSix (x = 0; 0.25; 0.5; 0.75 and 1) compounds have been theoretically studied using the full-potential linearized augmented plane wave (FP-LAPW) method within framework of the density functional theory. The generalized gradient approximation scheme as proposed by Wu-Cohen (GGA-WC) and Tran-Blaha modified Becke-Johnson exchange potential with improved parameterization by Koller are adopted for the treatment of electron exchange-correlation. All considered materials show half-metallic characteristics with semiconducting majority spin channel and metallic minority one. The total spin magnetic moment is 1μB for ternary alloys and 4μB for quaternary compounds. Our obtained results suggest that these materials could be promising candidate for spintronic applications.

Effect of Structure on the Electronic, Magnetic and Thermal Properties of Cubic Fe2MnxNi1−xSi Heusler Alloys

The concentration dependence of the phase stability, half-metallicity, thermal and magnetic properties of Fe2MnxNi1−xSi (0 ≤ x ≤ 1) Heusler alloys in two structures, Cu2MnAl (Fm3m) and Hg2TiCu (F43m), were investigated at the ab initio level using density functional theory. The exchange–correlation term was assessed using local spin density (LSDA) and generalized gradient approximation (GGA) along with Hubbard-U (U) corrections. Spin-polarized electronic band structure calculations for Fe2MnxNi1−xSi (0 ≤ x ≤ 1) alloys in their Cu2MnAl- and Hg2TiCu-structure have been carried out. These results indicate that the Hg2CuTi-type structure is more stable than the Cu2MnAl-type structure with increasing Mn content, from x = 0 to 0.25 using LSDA. No significant differences were observed using LSDA + U over GGA. The full Heusler compounds Fe2MnxNi1−xSi (0 ≤ x ≤ 1) are half metals in the Cu2MnAl-type structure for x = 0.75 and x = 1, and behave like a metal in the CuHg2Ti-type. The minority bands exhibit a band gap of about 0.11 (0.56) eV for Fe2Mn0.75Ni0.25Si using GGA (LSDA + U). Using the GGA scheme, the obtained band energy was smaller than that obtained by using the LSDA + U approach. These results clearly show that the lattice parameter, bulk modulus and total magnetic moment vary quadratically with Mn doping. The main contribution to the total magnetic moment comes from Mn or Fe atoms in B sites in both types of structures. The total magnetic moment of Fe2MnxNi1−xSi (0 ≤ x ≤ 1) alloys is typically in the range of 2–3 μB in the Cu2MnAl-Type and 3–4 μB in Hg2TiCu-Type per formula unit and consists of an average of 2 μB per Mn atom and less than 1 μB per Fe atom in the Cu2MnAl-Type, and an average of 2 μB per Mn atom and around 1 μB per Fe atom in the B site Hg2TiCu-Type. Using the quasi-harmonic Debye model, the concentration and temperature effects on the unit cell volume, thermal expansion coefficient, bulk modulus, the Debye temperature and heat capacity, for Fe2MnxNi1−xSi (0 ≤ x ≤ 1) Heusler alloys are investigated and analysed.

Ground-State Gas-Phase Structures of Inorganic Molecules Predicted by Density Functional Theory Methods.

We tested a battery of density functional theory (DFT) methods ranging from generalized gradient approximation (GGA) via meta-GGA to hybrid meta-GGA schemes as well as Møller–Plesset perturbation theory of the second order and a single and double excitation coupled-cluster (CCSD) theory for their ability to reproduce accurate gas-phase structures of di- and triatomic molecules derived from microwave spectroscopy. We obtained the most accurate molecular structures using the hybrid and hybrid meta-GGA approximations with B3PW91, APF, TPSSh, mPW1PW91, PBE0, mPW1PBE, B972, and B98 functionals, resulting in lowest errors. We recommend using these methods to predict accurate three-dimensional structures of inorganic molecules when intramolecular dispersion interactions play an insignificant role. The structures that the CCSD method predicts are of similar quality although at considerably larger computational cost. The structures that GGA and meta-GGA schemes predict are less accurate with the largest absolute errors detected with BLYP and M11-L, suggesting that these methods should not be used if accurate three-dimensional molecular structures are required. Because of numerical problems related to the integration of the exchange–correlation part of the functional and large scattering of errors, most of the Minnesota models tested, particularly MN12-L, M11, M06-L, SOGGA11, and VSXC, are also not recommended for geometry optimization. When maintaining a low computational budget is essential, the nonseparable gradient functional N12 might work within an acceptable range of error. As expected, the DFT-D3 dispersion correction had a negligible effect on the internuclear distances when combined with the functionals tested on nonweakly bonded di- and triatomic inorganic molecules. By contrast, the dispersion correction for the APF-D functional has been found to shorten the bonds significantly, up to 0.064 Å (AgI), in Ag halides, BaO, BaS, BaF, BaCl, Cu halides, and Li and Na halides and hydrides. These results do not agree well with very accurate structures derived from microwave spectroscopy; we therefore believe that the dispersion correction in the APF-D method should be reconsidered. Finally, we found that inaccurate structures can easily lead to errors of few kcal/mol in single-point energies.

Structural, electronic, elastic, vibrational and thermodynamic properties of U3Si2: A comprehensive study using DFT

Uranium silicide compound is a promising candidate as low enriched uranium nuclear fuel in light water reactors. Here we report a comprehensive study on structural, electronic, elastic, vibrational and thermodynamic properties of U3Si2 using plane wave based density functional theory. The electron-ion interaction and exchange-correlation energy terms have been described by projected-augmented wave method and generalized gradient approximation scheme, respectively. The relativistic corrections to the total energy have been accounted by incorporating the spin-orbit interactions in the total energy calculations. The results showed good agreement between the experimental and theoretical lattice parameters. The electronic structure of U3Si2 compound suggests significant contribution from the 5f and 3p orbitals of U and Si atoms at the Fermi energy level, respectively. The formation energy (ΔfH) of U3Si2 at 0 K, after zero point energy correction, have been estimated to be −37.40 kJ/mol. Elastic property calculation of U3Si2 showed mechanical stability and anisotropy at ambient pressure. In addition, the phonon calculation showed that U3Si2 is dynamically unstable. The temperature dependent thermodynamic properties of U3Si2 have also been evaluated using the phonon density of states.

Structural, electronic, elastic and thermodynamic properties of Li2ZrO3: A comprehensive study using DFT formalism

Lithium zirconate is considered to be potential tritium breeder material for fusion reactors. Here I report a comprehensive study on structural, electronic, elastic, and thermodynamic properties of Li2ZrO3 using plane wave based density functional theory. While the electron-ion interaction term has been described by projected-augmented wave method, the exchange-correlation energy was taken care of through generalized gradient approximation scheme. The optimized lattice and internal parameters of Li2ZrO3 unit cell agree well within ±1–2% from the experimental values. From the electronic structure analysis it is seen that the Fermi energy has significant contribution from the 2s, 2p and 4d orbitals of Li, O and Zr atoms, respectively. Elastic property calculation of Li2ZrO3 showed mechanical stability and anisotropy at ambient pressure. The formation energy (ΔfH) of Li2ZrO3 at 0 K, after zero point energy correction, has been estimated to be −1550 kJ/mol. The temperature dependent thermodynamic functions of Li2ZrO3 have also been calculated from the Debye-Grüneisen quasi-harmonic approximation and reported here.

Adsorption and decomposition of dimethyl methylphosphonate on pristine and mono-vacancy defected graphene: A first principles study

Here we report the adsorption and decomposition behavior of dimethyl methyl-phosphonate (DMMP) on pristine and defected graphene using the first principles theory. The primary objective of this study is to highlight the importance of a vacancy defect on the adsorption mechanism of a molecule. In order to account for the weak forces involved between the molecule and graphene, we have used dispersion corrected total energy calculations along with generalized gradient approximation scheme for the exchange correlation energy. Among various possible configurations, the most stable geometry shows oxygen atom of the DMMP molecule favors to be close to the surface plane and bind with one of the unsaturated carbon atoms at the defect site. The molecule-substrate interaction energy is stronger for defected graphene than pristine graphene. The decomposition of the DMMP molecule at the vacancy site of the defected graphene has been investigated. For the dissociative adsorption, it is seen that the CH bond of the DMMP breaks and H atom is transferred to one of the low-coordinated C-atoms at the vicinity of the defect, forming new CH bond. In addition, the CC bond formation between graphene and DMMP occurs. Finally, the nature of bonding and electronic structure at the interface was interpreted through site projected electronic density of states analysis.

Thermoelectric and mechanical properties of gapless Zr2MnAl compound

We present the study of elastic and magnetic properties of Zr2MnAl full-Heusler alloys within the first-principles density functional theory. The lattice constant, magnetic moment, bulk modulus and density of states are calculated using the full potential linearized augmented plane wave method in the generalized gradient approximation scheme. The thermoelectric properties are studied between the temperature range of 50–800 K. Seebeck coefficient (S) measurements indicate the material as n-type with large S value of −83.06 μV/K at 400 K. The material shows higher efficiency for thermoelectric use with figure of merit equal to 0.92 at 400 K relatively higher in comparison for the other full Heusler compounds in these temperature ranges. The behaviour of gapless character is mainly responsible for the anomalous transport properties of the material required for the thermoelectric applications.

First Principles Band-gap Calculations of 3d Transition Metals-added ZnO

The band-gaps of rock salt Zinc Oxide added with 3d transition metals (TM = Mn, Fe, Co, Ni) are estimated by Density Functional Theory (DFT) as implemented in the WIEN2k code. The Full Potential Linearized Augmented Plane Wave (FP-LAPW) method, within the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA) is employed, in order to find band-structures of Zn1-X(TM)XO alloys at x = 25%, 50%, and 75%. The results show metallic nature for all TM-doped ZnO alloys, contrary to the semiconducting nature as predicted by the experimentalists. This reveals an inadequacy of simple LDA and GGA schemes for band-gap calculations of highly correlated systems as in our case.

Expansion research on half-metallic materials in double perovskites of Sr2BB′O6 (B = Co, Cu, and Ni; B′ = Mo, W, Tc, and Re; and BB′ = FeTc)

Calculations with full structural optimization were conducted by generalized gradient approximation (GGA) with correlation effect correction (GGA+U) based on density functional theory. The stable structures, magnetic stable phases, and electronic structures of the double perovskites of Sr2BB′O6 (B=Co, Cu, and Ni; B′=Mo, W, Tc, and Re; and BB′=FeTc) were investigated. All compounds, except for Sr2NiMoO6 and Sr2NiWO6, can be half-metallic (HM) materials in the GGA scheme; Sr2NiMoO6 and Sr2NiWO6 are ferromagnetic (FM) insulators. Sr2FeTcO6, Sr2CoWO6, and Sr2NiTcO6 are stable ferrimagnetic (FiM)–HM compounds in the GGA and GGA+U schemes. Given the small energy difference between their antiferromagnetic and FiM states, Sr2CoTcO6, Sr2CuMoO6, Sr2NiMoO6, Sr2NiWO6, and Sr2NiReO6 can coexist. The mechanisms of the HM–FiM properties can be described by d–d′ hybridization with double-exchange interaction.