Full-potential Augmented Plane Wave Research Articles

Spin and Orbital Magnetisms of NiFe Compound: Density Functional Theory Study and Monte Carlo Simulation

The self-consistent ab initio calculations based on the density functional theory approach using the full potential linear augmented plane wave method are performed to investigate both the electronic and magnetic properties of the NiFe compound. Polarized spin within the framework of the ferromagnetic state between magnetic ions is considered. Also, magnetic moments considered to lie along (001) axes are computed. The Monte Carlo simulation is used to study the magnetic properties of NiFe. The transition temperature TC, hysteresis loop, coercive field and remanent magnetization of the NiFe compound are obtained using the Monte Carlo simulation.

Prediction of Half-Metallic Properties in Non-transition Metal-based Binary Compounds X Bi (X = Ba, Sr and Ca) with Zinc-Blende and Wurtzite Structures

In this study, structural, electronic and magnetic properties of non-transition metal-based binary compounds X Bi (X = Ba, Sr and Ca) in five different phases: rock salt, NiAs, wurtzite, zinc blende and CsCl, are investigated in order to find new sp magnetic materials used for real spintronic and other related applications. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW + lo) method within the spin density functional theory. As exchange-correlation potential, we used the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE) and the modified Becke-Johnson potential mBJ-GGA-PBE form. It is found that the magnetic moment in these compounds is mainly contributed by the spin-polarized p orbitals of Bi atoms. The WZ XBi are true half-metallic ferromagnet with opposite spin direction at Fermi energy having a magnetic moment of 2.00 μ B per formula unit.

Cation modified A2(Ba, Sr and Ca) ZnWO6 cubic double perovskites: A theoretical study

The cubic double perovskites A2ZnWO6 (A = Ba, Sr and Ca) are studied to understand the effect of A cation site, using the density functional theory (DFT) based full potential augmented plane wave method (FP-LAPW) with GGA and mBJ exchange correlation potentials. The structural robustness and stability are investigated using the bond lengths and the total energy. The band structure and density of states suggest that all these cubic double perovskites are indirect wide band gap semiconductors. The band gap varies from 3.90 eV (2.97 eV) for Ba2ZnWO6 system to 3.40 eV (2.8 eV) for Ca2ZnWO6 system using mBJ (GGA) exchange correlation potentials. Our studies suggest that A cation site modification has a strong effect on physical and electronic properties, in contrast to the structural robustness. The lattice parameter decreases from 8.19 Å to 7.9 Å from Ba to Ca at alkali cation site and the electronic band gap variation follows the common cation rule. The charge densities show enhanced localization of charges near the zinc and oxygen sites with increasing alkali cation atomic radii. In addition, we discuss the impact of A cation site modification on the dielectric and optical properties for A2ZnWO6 double perovskites.

Half-Metallic Ferromagnetism in Double Perovskite Ca2CoMoO6 Compound: DFT+U Calculations

A systematic investigation on magnetism and spin-resolved electronic properties in double perovskite Ca2CoMoO6 compound was performed by using the full-potential augmented plane wave plus local orbitals (APW[Formula: see text]) method within the generalized gradient approximation (GGA-PBE) and GGA-PBE[Formula: see text] scheme. The stability of monoclinic phase ([Formula: see text] #14) relative to the tetragonal ([Formula: see text]#87) and cubic ([Formula: see text] #225) phase is evaluated. We investigate the effect of Hubbard parameter [Formula: see text]on the ground-state structural and electronic properties of Ca2CoMoO6 compound. We found that the ferromagnetic ground state is the most stable magnetic configuration. The calculated spin-polarized band structures and densities of states indicate that the Ca2CoMoO6 compound is half-metallic (HM) and half-semiconductor (HSC) ferromagnetic (FM) semiconductor with a total magnetic moment of 6.0 using GGA-PBE and GGA-PBE[Formula: see text], respectively. The Hubbard [Formula: see text] parameter provides better description of the electronic structure. Using the Vampire code, an estimation of exchange couplings and magnetic Curie temperature is calculated. Further, our results regarding the magnetic properties of this compound reveal their ferromagnetic nature. The GGA-PBE[Formula: see text] approach provides better band gap results as compared to GGA-PBE approximation. These results imply that Ca2CoMoO6 could be a promising magnetic semiconductor for application in spintronic devices.

Structural Stability, Electronic and Magnetic Properties of (Ni1−xCox)2MnSn Quaternary Heusler Alloys

In this study, we present the calculated structural, electronic and magnetic properties of mixed Heusler alloys (Ni[Formula: see text]Co[Formula: see text]MnSn. Using ab initio calculations with the full-potential augmented plane-wave method (FP-LAPW), we evaluated the various possible configurations of Ni and Co sites in the (Ni[Formula: see text]Co[Formula: see text]MnSn crystallographic lattice. The lowest energy configuration is determined based on energetic considerations. The calculated equilibrium lattice parameters and magnetic moments are in a reasonable agreement with available experimental data. Of interest, we found that the change of total magnetic moment can be interpreted as a linear variation of the magnetic moment of manganese and cobalt atoms.

Theoretical analysis of the electronic, optical and thermal properties of lead strontium telluride alloys Pb1−xSrxTe (x = 0.0−1.0)

We have simulated different physical properties of Pb1−xSrxTe semiconductors, using the Ab-initio full potential augmented plane wave (FP-LAPW) method. The two commonly used exchange potentials viz., PBE-GGA and WC-GGA are used along with the most recently developed modified Becke and Johnson (mBJ) potential to study the electronic and optical properties. In this study, we have observed an increase in band gap values as well as the lattice parameter with increasing the concentration of Sr atoms in Pb1−xSrxTe alloys while the bulk modulus and the refractive index have reverse effect. The microscopic origin of the band gap bowing is explained using the approach of Zunger and co-workers. At ambient conditions (p = 0, T = 0), the calculations indicate that Pb1−xSrxTe is a direct band gap semiconductor R–R with x = 0.125, 0.25, 0.375, 0.5, 0.625, 0.75 and 0.875. The refractive indices are also calculated using the FP-LAPW method and the models of Moss, Ravindra and the Herve–Vandame. The obtained results are in consistent with the previous available data. To study the thermal effects, the temperature effect on the lattice parameters, thermal expansions, heat capacities the quasi-harmonic Debye model is applied. The Debye temperature is determined from the non-equilibrium Gibbs function.

Theoretical analysis of the structural, electronic and optical properties of tetragonal Sr2GaSbO6

Structural, electronic and optical properties of the tetragonal structure Sr2GaSbO6 compound have been investigated using a full relativistic version of the full-potential augmented plane-wave method. 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 lattice parameters (a, c) are optimized and found in good agreements with the available experimental data. Results are given for bulk modulus B and the pressure derivative of the bulk modulus B’. Band structure and densities of states (DOS) of tetragonal Sr2GaSbO6 have been obtained. The EV-GGA scheme was selected to obtain better band gap value (1.00 eV) as compared to GGA-PBE (0.75 eV). Furthermore, in order to clarify the mechanism of optical transitions of tetragonal Sr2GaSbO6, the complex dielectric function, refractive index and extinction coefficient were calculated for radiation up to 20 eV.

FP-(L)APW + lo study of mechanical stability and electronic behavior of CoGe in B20 structure

AbstractThe aim of this work is a theoretical study of structural, elastic, electronic and thermal properties of CoGe compound in B20 structure using All-electron self-consistent Full Potential Augmented Plane Waves plus local orbital “FP(L)APW + lo” within the framework of Density Functional Theory DFT. GGA-PBEsol is the exchange-correlation potential selected in this work. This choice is motivated by the success of this functional in predicting structural and mechanical properties of solids. The values obtained by the study of structural properties are in very good agreement with those found previously. In this work, the elastic constants have been predicted for the first time and the obtained values confirm the mechanical stability of the CoGe compound in its B20 structure. The electronic part of this work shows that CoGe has metallic behavior with a mixed bonding between cobalt and germanium of covalent-metallic type. The effect of temperature and hydrostatic pressure on the lattice parameter - a0, heat capacity at constant volume - CV, thermal expansion coefficient - α and entropy - S of the CoGe have been studied using Debye model.

Polymorph phosphor SrSi2O2N2:Eu2+ optoelectronic properties for highly efficient LED: ab-initio calculations

A doped europium polymorph based on phosphor with a structure of SrSi2O2N2 was investigated using the density functional theory as implemented in the full potential linear augmented plane wave method. The exchange correlation was described within the generalized gradient approximation added to the optimized effective Hubbard parameter. The optoelectronic properties were reported to explore the possibility to use SrSi2O2N2:Eu2+ for light-emitting diodes (LED) devices. The electronic band gap was reduced from the parent SrSi2O2N2, 6.646eV to 4.66eV when europium was incorporated and it is a direct band gap. The densities of states have shown the role of europium and its f-orbitals in tuning the band gap. Optical properties, such as optical reflectivity, refractive index and electron energy loss, were deduced from the dielectric function for radiation up to 15 eV. The present calculations suggest clearly that SrSi2O2N2:Eu2 is a promising compound for LEDs devices.

One-hundred-three compound band-structure benchmark of post-self-consistent spin-orbit coupling treatments in density functional theory

We quantify the accuracy of different non-self-consistent and self-consistent spin-orbit coupling (SOC) treatments in Kohn-Sham and hybrid density-functional theory by providing a band structure benchmark set for the valence and low-lying conduction energy bands of 103 inorganic compounds, covering chemical elements up to Po. Reference energy band structures for the PBE density functional are obtained using the full-potential (linearized) augmented plane wave code Wien2k, employing its self-consistent treatment of SOC including Dirac-like p$^{1/2}$ orbitals in the basis set. We use this benchmark set to benchmark a computationally simpler, non-self-consistent all-electron treatment of SOC based on scalar-relativistic orbitals and numeric atom-centered orbital basis functions. For elements up to Z$\approx$50, both treatments agree virtually exactly. For the heaviest elements considered (Tl, Pb, Bi, Po), the band structure changes due to SOC are captured with a relative deviation of 11% or less. For different density functionals (PBE vs. the hybrid HSE06), we show that the effect of spin-orbit coupling is usually similar but can be dissimilar if the qualitative features of the predicted underlying scalar-relativistic band structures do not agree. All band structures considered in this work are available online via the NOMAD Repository to aid in future benchmark studies and methods development.

First-principles calculations of pressure and temperature dependence of thermodynamic properties of anti-perovskite BiNBa3compound

The structural, elastic and thermodynamic properties of the antiperovskite BiNBa3 compound are studied under the effects of pressure and temperature using the full-potential augmented plane wave plus the local orbitals method (FP-APW+lo). The exchange–correlation potential is treated using the generalized gradient approximation within the Perdew, Burke and Ernzerh scheme (GGA-PBE). The calculated lattice constants, the bulk moduli and their pressure derivatives are in reasonable agreement with the available data. The elastic constants Cij and interrelated quantities have also been calculated. The thermodynamic quantities under pressure and temperature are also calculated and elaborated upon.

Cu substituted CeCo5: New optimal permanent magnetic material with reduced criticality

A comprehensive theoretical prediction using a mechanism of site substitution confirms the crucial role of Cu in enhancing the capabilities of CeCo5 as a competitive magnet with its known high coercivity. A remarkable enhancement of magnetic anisotropy energy (MAE) of 3.09 meV/f.u. and 2.94 meV/f.u. without significant decrease of magnetic moment is found for 10% and 5% Cu substitution at 2c sites of the hexagonal lattice. Calculations predict the increment of coercivity and magnetocrystalline anisotropy (1.6 times) compared to pristine CeCo5. The exceptional enhancement in MAE is due to the formation of asymmetric charge hybridization among the Cu (2c) and Co (both 2c and 3g) sites along the uniaxial direction. Because of this asymmetric charge distribution environment, the intrinsic behavior of Ce adjacent to Cu changes abruptly making them more uniaxial and magnetically enhanced creating mixed valence states. For these calculations, we have employed the full-potential augmented plane wave method in conjunction with spin orbit coupling.

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

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

Elastic stability and optical property under pressure of TiN phases: by first principles study

The electronic and optical properties of the rock-salt, CsCl-type, zinc-blende and wurtzite phases of TiN have been calculated by First-Principles study for relaxed and under pressure conditions. Calculations are based on the density functional theory and full potential augmented plane waves method by Generalized Gradient Approximation. The optical transitions in zero pressure are derived from the density of states and dielectric function. In addition, various optical characters, such as reflectivity, refraction and extinction indices, under positive and negative pressures are compared and contrasted. It is found that all mentioned phases of TiN are elastically stable and exhibit a rising trend in their plasmonic frequencies by increasing the pressure imposed on.

Electronic structure and optical properties of iron based chalcogenide FeX2 (X = S, Se, Te) for photovoltaic applications: a first principle study

In present work, the electronic structure and optical properties of the FeX2 (X = S, Se, Te) compounds have been evaluated by the density functional theory based on the scalar-relativistic full potential linear augmented plane wave method via Wien2K. From the total energy calculations, it has been found that all the compounds have direct band nature, which determined by iron 3d states at valance band edge and anion p dominated at conduction band at Γ-point and the fundamental band gap between the valence band and conduction band are estimated 1.40, 1.02 and 0.88 eV respectively with scissor correction for FeS2, FeSe2 and FeTe2 which are close to the experimental values. The optical properties such as dielectric tensor components and the absorption coefficient of these materials are determined in order to investigate their usefulness in photovoltaic applications.

Structural, elastic and magneto-electronic properties of half-metallic BaNpO3 perovskite

First principles calculations on structural, electronic, magnetic and elastic properties of BaNpO3 oxide are reported using full potential augmented plane wave method. To achieve the optimized lattice parameters, the local density approximation (LDA) and generalized gradient approximation (GGA) have been used. The calculated values of lattice constant and bulk modulus are found to be in agreement with experimental and other reported results. In addition, Hubbard approximation potential (GGA + U) and modified Becke Johnson approximation (mBJ) are also engaged for the exact prediction of band structure. Half-metallicity along with 100% spin polarization is reflected from the spin resolved band structures as well as densities of states. The ferromagnetic stable configuration of BaNpO3 perovskite is observed from the double cell optimization method as well as the spin-magnetic moment calculations. In addition, elastic constants have been calculated to envisage the mechanical response of this material. From these mechanical parameters, the ductile nature of the material is observed along with a Debye temperature of 356 K and melting temperature of 1968.71 K.

Exploring the optoelectronic properties of Nitrido-magneso-silicates: Ca[Mg3SiN4], Sr[Mg3SiN4], and Eu[Mg3SiN4

Optoelectronic properties of the Nitrido-magneso-silicates Ca[Mg3SiN4], Sr[Mg3SiN4], and Eu[Mg3SiN4] compounds have been investigated using the relativistic full-potential augmented plane-wave method (FLAPW) based on the density functional theory (DFT). The calculations of the electronic and optical properties were conducted by using the local density approximation (LDA), generalized gradient approximation (GGA), and modified Becke Johnson (mBJ) potential. A study of the band structures shows that these compounds are indirect band gap materials. We found a great variation in the obtained energy band gap value as we changed the functionals. The mBJ functional leads to a greater band-gap value compared to LDA and GGA cases. Based on the calculated electronic structure, the optical properties computed, such as the complex dielectric function, absorption coefficient, reflectivity, energy loss function and refractive index, were functions of the photon energy. Origins of the spectral peaks in the optical spectra were discussed and assigned to different electronic transitions observed from the electronic structure calculation.

Electronic and magnetic properties of antiferromagnetic TbAs via modified Becke Johnson potential plus an on-site Coulomb U

In this work, theoretical study of structural, elastic, electronic properties and magnetic ordering of Terbium arsenide (TbAs) in NaCl-B1 and CsCl-B2 phases are investigated using first-principles calculations based on the full-potential augmented plane wave plus local orbitals (FP-L/APW ‏+ lo) method within the framework of density functional theory (DFT) in the generalized gradient approximation (GGA) with the on-site Hubbard Ueff parameter (GGA+U). At ambient conditions Terbium monopnictides stabilize in NaCl (B1) structure. The calculations indicate that there exists a phase transition from the NaCl-type (B1) structure to CsCl-type (B2) structure at the transition pressure of 16GPa. The calculated structural parameters, such as the lattice constant, bulk modulus and second-order elastic constants, are presented. Elastic constants and their related parameters such as Poisson's ratio, Young modulus and shear modulus were calculated. The anti-ferromagnetic of type II state is found to be the most stable than the other possible phases, which is in agreement with experiment. By varying the Hubbard U parameter from 0 to 10eV, a detailed study of magnetism of this compound via the density of states DOS, is presented. We find that semiconducting band structures can be obtained using the modified Becke-Johnson potential plus an on-site Coulomb U (the mBJ+U approach).

A first principles study of the electronic structure, elastic and thermal properties of UB2

Uranium diboride (UB2) has been widely deployed for refractory use and is a proposed material for Accident Tolerant Fuel (ATF) due to its high thermal conductivity. However, the applicability of UB2 towards high temperature usage in a nuclear reactor requires the need to investigate the thermomechanical properties, and recent studies have failed in highlighting applicable properties. In this work, we present an in-depth theoretical outlook of the structural and thermophysical properties of UB2, including but not limited to elastic, electronic and thermal transport properties. These calculations were performed within the framework of Density Functional Theory (DFT) + U approach, using Quantum ESPRESSO (QE) code considering the addition of Coulomb correlations on the uranium atom. The phonon spectra and elastic constant analysis show the dynamic and mechanical stability of UB2 structure respectively. The electronic structure of UB2 was investigated using full potential linear augmented plane waves plus local orbitals method (FP-LAPW+lo) as implemented in WIEN2k code. The absence of a band gap in the total and partial density of states confirms the metallic nature while the valence electron density plot reveals the presence of covalent bond between adjacent B-B atoms. We predicted the lattice thermal conductivity (kL) by solving Boltzmann Transport Equation (BTE) using ShengBTE. The second order harmonic and third-order anharmonic interatomic force constants required as input to ShengBTE was calculated using the Density-functional perturbation theory (DFPT). However, we predicted the electronic thermal conductivity (kel) using Wiedemann-Franz law as implemented in Boltztrap code. We also show that the sound velocity along ‘a’ and ‘c’ axes exhibit high anisotropy, which accounts for the anisotropic thermal conductivity of UB2.

The full-potential study of ErMg

The structural, electronic and magnetic properties of ErMg are investigated using the full potential linear augmented plane wave method based on density functional theory. The calculated structural parameters using LDA are in excellent agreement with the available experimental result. The calculated band structure is at 0 GPa. The valence and conduction bands are overlapped notable at the Fermi level (EF = 0 eV). Consequently, there is no energy gap. The calculated band structure shows that this alloy has metallic nature. Total magnetic moment at equilibrium lattice constant of ErMg intermetallic in B2 phase along with the magnetic moment on the atomic and interstitial sites have also been presented in this paper.