Linear Augmented Plane Wave Method Research Articles

Electronic and Magnetic Properties of Co2CrGa1−x Si x Heusler Alloys

First-principles calculations within full-potential linear-augmented plane-wave method using the generalized gradient approximation were carried out for the electronic and magnetic properties of the Co2CrGa1−xSix Heusler alloys. The electronic structure calculations show a conservation of the minority spin gap supporting the half-metallic character of the Co2CrGa1−xSix alloys. The substitution of Ga by Si results in linear increasing of total magnetic moment as silicon concentration increases following the Slater–Pauling rule that is in agreement with experimental data.

A Comparison of the~Structural, Electronic, Optical and Elastic Properties of Wurtzite, Zinc-Blende and Rock Salt TlN: A DFT Study

In this article we investigated structural, electronic, elastic, and optical properties of TlN in three phases, using full potential linear augmented plane wave method in the density functional theory frame with WIEN2k code. The calculations have been done in the generalized Perdew‐Burke‐Ernzerhof generalized gradient approximation, the generalized Wu‐Cohen gradient approximation, the generalized Perdew‐Burke‐Ernzerhof solid gradient approximation, local density approximation, and the modified Becke‐Johnson approximations. In spite of the absence of any experimental data for TlN, our results are compared with other results achieved by other dierent approximations which shows a good agreement with them. The band gap for TlN in wurtzite and zinc-blende are obtained to be 0.07 and 0.09 eV within modified Becke‐Johnson‐local density approximation+spin‐orbit approximation, respectively. The structural properties such as phase transitions, equilibrium lattice parameters, bulk modulus and its first pressure derivative were obtained using an optimization method. Moreover, we calculated quantities such as elastic constants, the Young modulus, shear modulus, the Poisson ratio, and sound velocities for longitudinal and transverse waves, the Debye temperature and the Kleinman parameters in dierent approximations and we show that TlN is softer than other nitrides of the III-group. The static calculations predicted that wurtzite to rock salt and zinc-blende to rock salt phase transitions occur at 14.7 GPa and 15.8, respectively. The optical properties of TlN in three phases, calculated in generalized gradient approximation and local density approximation and imaginary part of dielectric function show that TlN in wurtzite and zinc-blende phases have semiconductor properties but rock salt phase do not show. As well as, we investigate the influence of the hydrostatic pressure on the elastic parameters and energy band structures for TlN (zinc-blende) within local density approximation.

Structural and thermoelectric properties of zintl-phase CaLiPn (Pn=As, Sb, Bi)

First-principles calculations were carried out to study the structural, mechanical, dynamical and transport properties of zintl phase materials CaLiPn (Pn=As, Sb and Bi). We have used two different approaches to solve the system based on density functional theory. The plane wave pseudopotential approach has been used to study the structural and dynamical properties whereas, full potential linear augment plane wave method is used to examine the electronic structure, mechanical and thermoelectric properties. The calculated ground-state properties agree quite well with experimental values. The computed electronic structure shows the investigated compounds to be direct band gap semiconductors. Further, we have calculated the thermoelectric properties of all the investigated compounds for both the carriers at various temperatures. We found a high thermopower for both the carriers, especially n-type doping to be more favourable, which enabled us to predict that CaLiPn might have promising applications as a good thermoelectric material. Further, the phonon dispersion curves of the investigated compounds showed flat phonon modes and we also find lower optical and acoustic modes to cut each other at the lower frequency range, which further indicate the investigated compounds to possess reasonably low thermal conductivity. We have also analysed the low value of the thermal conductivity through the empirical relations and discussions are presented here.

First Principles Study of Structural and Electronic Properties of ErX (X=Cu, Ag and Au) Intermetallics

The electronic structures, densities of states and Fermi surfaces of ErX (X = Cu, Ag and Au) intermetallic compounds are studied using full potential linear augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA) for the exchange-correlation functional. The total energies are computed as a function of volume and fitted to the Birch equation of state. The ground state properties such as equilibrium lattice constants (a0), bulk modulus (B) and pressure derivative of bulk modulus (B') and density of states at the Fermi level N (EF) are calculated. The states at the Fermi level (EF) are dominated by Er ‘d’ states with significant contribution of ‘p’ and ‘d’ states of X. We have also plotted charge density and Fermi surface to study the bonding properties of ErX compounds.

Extension of the basis set of linearized augmented plane wave (LAPW) method by using supplemented tight binding basis functions.

In order to increase the accuracy of the linearized augmented plane wave (LAPW) method, we present a new approach where the plane wave basis function is augmented by two different atomic radial components constructed at two different linearization energies corresponding to two different electron bands (or energy windows). We demonstrate that this case can be reduced to the standard treatment within the LAPW paradigm where the usual basis set is enriched by the basis functions of the tight binding type, which go to zero with zero derivative at the sphere boundary. We show that the task is closely related with the problem of extended core states which is currently solved by applying the LAPW method with local orbitals (LAPW+LO). In comparison with LAPW+LO, the number of supplemented basis functions in our approach is doubled, which opens up a new channel for the extension of the LAPW and LAPW+LO basis sets. The appearance of new supplemented basis functions absent in the LAPW+LO treatment is closely related with the existence of the u̇l-component in the canonical LAPW method. We discuss properties of additional tight binding basis functions and apply the extended basis set for computation of electron energy bands of lanthanum (face and body centered structures) and hexagonal close packed lattice of cadmium. We demonstrate that the new treatment gives lower total energies in comparison with both canonical LAPW and LAPW+LO, with the energy difference more pronounced for intermediate and poor LAPW basis sets.

Electronic and Magnetic Properties of Ca-Doped Mn-Ferrite

Spinel ferrite structures have vast applications, from microwave to radio frequencies. In order to acquire new electronic and optical behavior, divalent cations can be added to normal spinel ferrite structure. This way it is possible to facilitate its usage in material and science technology. In this work we have analyzed the impact of Ca addition to normal spinel manganese ferrite on electronic and magnetic properties by the first-principles calculations. For the exchange-correlation functional, Wu-Cohen, generalized gradient approximation method was used for electron-electron interactions. The calculation of electronic band structures is based on full potential linear augmented plane wave method. The calculated density of states shows that the addition of Ca ions has a significant impacts on the electronic and magnetic structure.

Optoelectronic structure and related transport properties of BiCuSeO-based oxychalcogenides: First principle calculations

Recent experiments have revealed that the p-type BiCuSeO-based oxychalcogenides compounds exhibit a high thermoelectric figures of merit due to their very low lattice thermal conductivities and moderate Seebeck coefficient in the medium temperature range. In the present work, we reported on the optoelectronic and thermoelectric properties using the full potential linear augmented plane wave method and modified Becke-Johnson potential with spin-orbit coupling. The properties show that the BiCuSeO-based oxychalcogenides exhibit a semiconductor behavior with band gap values of 0.51, 0.45 and 0.41 eV for BiCuSO, BiCuSeO, and BiCuTeO, respectively. Due to their prominent role for thermoelectric applications, we combined Boltzmann transport theory to DFT results to compute the transport properties, mainly electronic conductivity, thermal conductivity, Seebeck coefficient and power factor. The present results show the dominance of BiCuTeO for thermoelectric application compared to the BiCuSO and BiCuSeO.

Ab initio calculations of optical properties of silver clusters: cross-over from molecular to nanoscale behavior

Electronic and optical properties of silver clusters were calculated using two different \textit{ab initio} approaches: 1) based on all-electron full-potential linearized-augmented plane-wave method and 2) local basis function pseudopotential approach. Agreement is found between the two methods for small and intermediate sized clusters for which the former method is limited due to its all-electron formulation. The latter, due to non-periodic boundary conditions, is the more natural approach to simulate small clusters. The effect of cluster size is then explored using the local basis function approach. We find that as the cluster size increases, the electronic structure undergoes a transition from molecular behavior to nanoparticle behavior at a cluster size of 140 atoms (diameter $\sim 1.7$\,nm). Above this cluster size the step-like electronic structure, evident as several features in the imaginary part of the polarizability of all clusters smaller than Ag$_\mathrm{147}$, gives way to a dominant plasmon peak localized at wavelengths 350\,nm$\le\lambda\le$ 600\,nm. It is, thus, at this length-scale that the conduction electrons' collective oscillations that are responsible for plasmonic resonances begin to dominate the opto-electronic properties of silver nanoclusters.

Electronic band structure and optoelectronic properties of double perovskite Sr2MgMoO6 through modified Becke-Johnson potential

The crystal structure, electronic and optical properties of double perovskite Sr2MgMoO6 have been calculated by using the full-potential linear augmented plane wave (FP-LAPW) method. The band structure and density of states (DOS) were carried out by the modified Becke–Johnson (mBJ) exchange potential approximation based on the density functional theory (DFT). The calculated band structure shows a direct band gap (Γ–Γ) of 2.663eV for Sr2MgMoO6. The compound Sr2MgMoO6 has a triclinic structure with the space group I-1, the lattice parameters a=5.5666Å, b=5.5661Å and c=7.9191Å, which are used in our calculations. The optical parameters, like dielectric constant, refractive index, reflectivity and energy loss function were also calculated and analyzed. This work provides the first quantitative theoretical prediction of the optical properties and electronic structure for the triclinic phase of Sr2MgMoO6.

Exploring the thermoelectric and magnetic properties of uranium selenides: Tl2Ag2USe4 and Tl3Cu4USe6

The electronic, magnetic and thermoelectric properties of Tl2Ag2USe4 and Tl3Cu4USe6 compounds were investigated using the full potential linear augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The exchange correlation was treated with the generalized gradient approximation plus optimized effective Hubbard parameter and spin–orbit coupling (GGA+U+SOC). The present uranium selenides show narrow direct energy band gap values of 0.7 and 0.875eV for Tl2Ag2USe4 and Tl3Cu4USe6 respectively. For both selenides U-d/f states are responsible for electrical transport properties. Uranium atoms were the most contributors in the magnetic moment compared to other atoms and show ferromagnetic nature. The spin density isosurfaces show the polarization of neighboring atoms of Uranium, such as silver/copper and selenium. Thermoelectric calculations reveal that Tl3Cu4USe6 is more suitable for thermoelectric device applications than Tl2Ag2USe4.

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.

THEORETICAL INVESTIGATIONS OF β-TRICALCIUM PHOSPHATE BIOMATERIALS: DFT INSIGHT

Beta-tri-calcium phosphate (β-TCP) materials have gained a great deal of research considerations in biomaterial area due to their excellent biocompatibility and identical chemical compositions to the natural teeth and bones. Therefore, the β-TCP compound can be used as coatings, cement and composites as well as biocompatible ceramics for medical and dental applications. Electronic and optical properties for β-TCP compound have been investigated using density functional theory (DFT). For the calculations, we used full potential linear augmented plane wave method (FPLAPW), within three types of approximations along with local density approximations (LDA), generalized gradient approximations (GGA) and Modified Becke-Johnson (mBJ) to get the effect of the exchange and correlation in our calculations to get an accurate results. The computed band gap values for (β-TCP) compound using LDA, GGA, and mBJ-GGA approximations are 5.5 eV, 5.9 eV and 6.8 eV respectively. This is also predicted that the chemical bonding in this compound is a kind of combination of covalent and ionic character that is in a line with the experimental findings. The optical parameter, static dielectric constant ε1(0) reaches the values of 3.23681 (eV) at 0 GPa for the β-TCP compound. The obtained results are of vital nature for rising the quality of the electronic and optical properties of this material, and provide more evidence to fabricate novel Beta-Tri-calcium phosphate biomaterials for medical and dental applications.

Electronic structure and thermoelectricity of filled skutterudite CeRu4Sb12

First-principles calculations of the energy band structure and density of states of filled skutterudite CeRu4Sb12 have been performed to understand the origin of thermoelectricity. The calculations are carried out using the full potential linear augmented plane wave (FP-LAPW) method within a framework of LDA approach. CeRu4Sb12 is a metal with bands crossing Fermi energy level more than twice with indirect energy band gap of ∼0.09 eV above the Fermi energy level. The study of the elastic properties suggests the ductile nature of the material with covalent contribution in the atomic bonding. Our calculations performed for the density of electronic states near the Fermi energy level show that the large thermo-power at room temperature originates from the hybridized Ru-d and Sb-p orbitals. The study of the thermal transport properties suggests the high value of Seebeck coefficient with figure of merit (ZT) = 0.12, which is consistent to the values obtained for the analogous compounds.

DENSITY FUNCTIONAL THEORY STUDY OF THE ELECTRONIC AND OPTICAL PROPERTIES OF PURE AND MAGNESIUM DOPED Β-TRICALCIUM PHOSPHATE COMPOUND

β-Tri-calcium phosphate material (β-TCP), have attract a wide interest in the material science and medical science applications, due to its excellent biocompatibility and its identical chemical compositions to the natural teeth and bones. For that reason, (β-TCP) compound is widely used as biocompatible ceramics in medical and dental science applications. However, research shows that, pure β-TCP material has lower ability to stimulate the growth of natural bone and teeth as needed. Therefore, in order to address this deficiency magnesium impurity is used to replace calcium in the matrix of pure β-TCP to enhance its electronic and optical properties which are not present in the pure one. Thereby, its biological performance becomes improved. By changing the chemical composition of β-TCP to be similar to the mineral compositions of the natural teeth and bones. This will give more insight in fabrication of biomaterial devices for replacing, repairing and rebuilding the broken or damaged human teeth and bones. Here, we present the study of compound β-TCP using density functional theory (DFT). For the calculations, we used full potential linear augmented plane wave method (FPL-APW), along with generalized gradient approximations (GGA) potential. The band gap values of 5.2 eV and 3.4 eV are obtained for the pure and Mg-doped β-TCP, respectively. These results are in good agreement with the experimental values. Our results show peaks which correspond to the refractive index, complex dielectric function, optical conductivity, optical reflectivity, extinction coefficient, absorption efficient, and electron energy loss. These peaks are shifted towards the higher energy values for the pure and Mg-doped β-TCP material. The obtained results have more significance for increasing the quality of electronic and optical properties of this material and offer more evidences to synthesize enhanced β-TCP material for dental and medical applications.

Ab initio study of structural, mechanical, thermal and electronic properties of perovskites Sr(Li,Pd)H3

The structural, elastic, thermal and electronic properties of perovskite hydrides SrLiH3 and SrPdH3 have been investigated using the all-electron full-potential linear augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The present results are in good agreement with available theoretical and experimental data. The three independent elastic constants [Formula: see text], [Formula: see text] and [Formula: see text] are also reported. From electronic band structure and density of states (DOSs), it is found that SrLiH3 is an insulator characterized by an indirect gap of 3.48 eV, while SrPdH3 is metallic with a calculated DOSs at Fermi energy of 0.745 states/eV-unit cell. Poisson’s ratio [Formula: see text], Young’s modulus (E), shear modulus (G), anisotropy factor (A), average sound velocities [Formula: see text] and density [Formula: see text] of these compounds are also estimated for the first time. The Debye temperature is deduced from the average sound velocity. Variation of elastic constants and bulk modulus of these compounds as a function of pressure is also reported. Pressure and thermal effects on some macroscopic properties are predicted using the quasi-harmonic Debye model.

Investigations of the Structural, Electronic, Magnetic, and Half-Metallic Behavior of Co2MnZ (Z = Al, Ge, Si, Ga) Full-Heusler Compounds

The structural, electronic, and magnetic properties of the full-Heusler compounds Co2MnZ (Z = Al, Ge, Si, Ga) have been investigated using the first-principles calculations with the full-potential linear-augmented plane wave method within the density functional theory. The electronic structures and magnetic properties of the Co2MnZ (Z = Al, Ge, Si, Ga) compounds with both Hg2CuTi- and Cu2MnAl-type structures are studied. It is found that the calculated lattice constants are in good agreement with the theoretical values. Using the general gradient approximation, we observe that the Cu2MnAl-type structure is more stable than the Hg2CuTi type. The Co2MnZ (Z = Al, Ge, Si, Ga) compounds were half-metallic ferromagnets in the Cu2MnAl-type structure. The total magnetic moments of the Co2MnZ (Z = Al, Ge, Si, Ga) compounds in the Cu2MnAl-type structure were 4, 5, 5, and 4 μB, respectively, which is in agreement with the Slater-Pauling rule, m = NV−24 Furthermore, the origin for the appearance of the half-metallic band gap in the Co2MnZ compound was also discussed which shows them to be promising materials for possible spintronics applications.

Влияние энергий взаимодействия между атомами углерода в ГЦК-железе на концентрационную зависимость активности углерода

The first-principle simulation of the interaction energies of carbon atoms in FCC iron was carried out using the software package WIEN2k. They amounted to E 1 = 0.06 eV, E 2 = 0.1 eV and E 3 = 0.005 eV (interaction energies between carbon atoms located on the first, second and third spheres of coordination of interstitial sublattice of FCC iron). The full potential linear augmented plane-wave (LAPW) method within the generalized gradient approximation PBE-GGA in the supercell of 32 iron atoms with periodic boundary conditions was used in the investigation. This is the most powerful technique in the framework of Density Functional Theory. In order to check the reliability of found energy values, the concentration dependence of carbon activity in FCC iron was built using Monte-Carlo simulation. The good qualitative agreement of activity curve obtained with our interaction energies with the experimental one indicates the reliability of C–C interaction energy and performance of our model of paramagnetic state. Accounting of data on interaction on the third sphere of coordination does not significantly affect the calculation results. This is due to a very low value of the interaction energy of carbon atoms in FCC-iron on the third sphere of coordination.

Electronic Correlations Effects and Magnetic Properties in Manganese–Bismuth Compound

Self-consistent ab initio calculations, based on the density functional theory approach and using the full potential linear augmented plane wave method, are performed to investigate both electronic and magnetic properties of the MnBi compounds. Polarized spin and spin–orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. The magnetic moment considered to lie along (001) axes are computed. The obtained data from ab initio calculations are used as input for the high-temperature series expansions calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Mn–Mn in MnBi are given using the mean field theory. The high-temperature series expansions of the Ising model magnetic susceptibility is given up to the tenth order series in x = J1(Mn–Mn) / kBT. The Curie temperature, TC, is obtained using high-temperature series expansions of the magnetic susceptibility series combined with the Pade approximant method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.

Predicted thermoelectric properties of olivine-type Fe2GeCh4 (Ch = S, Se and Te)

We present here the thermoelectric properties of olivine-type Fe2GeCh4 (Ch = S, Se and Te) using the linear augmented plane wave method based on first principles density functional calculations. The calculated transport properties using the semi-local Boltzmann transport equation reveal very high thermopower for both S and Se-based compounds compared to their Te counterparts. The main reason for this high thermopower is the quasi-flat nature of the bands at the valence and conduction band edges. The calculated thermopower of Fe2GeS4 is in good agreement with the experimental reports at room temperature, with the carrier concentration around 1018–1019cm−3. All the investigated systems show an anisotropic nature in their electrical conductivity, resulting in a value less than the order of 102 along the a-axis compared to the b- and c-axes. Among the studied compounds, Fe2GeS4 and Fe2GeSe4 emerge as promising candidates with good thermoelectric performance.

Spontaneous Polarization and Magnetic Investigation Of BiXO3 (X=Co, Mn, Fe, V, Zn): First-Principle Study

Spontaneous polarization and magnetic properties of BiXO3 with X = Co, Fe, Mn, V, and Zn have been studied using the full-potential, linear augmented plane wave (FP-LAPW) method with GGA and mBJ implemented in the WIEN2K code. The investigation shows that BiXO3 with X = Co, Fe, Mn, and Zn is stable in the antiferromagnetic state while for BiVO3, the magnetic stability was shown in the ferromagnetic state. The calculation shows the existence of a charge transfer between p states of oxygen and d states of Co and Fe for X = Co and Fe. The existence of Co, Fe, Mn, and V makes BiXO3 a non-absorbent compound. However, for Zn, the structure behaves as an absorbent compound especially in the visible light. We note that the spontaneous polarization is calculated with Berry phase BI and was found very close and comparable with other works.