Full Potential Linearized Augmented Plane Wave Calculations Research Articles

An ab initio investigation of LiCoBO3 as Li-ion battery cathode material

We give a first principles approach for the structural, electronic and magnetic properties of LiCoBO3 and CoBO3 in the monoclinic lattices. Along [001] direction, based on density functional theory approach and using Full Potential Linear Augmented Plane Wave (FP-LAPW) method, Polarized spin and spin–orbit coupling are included in calculations, and major spin was set up. The calculations were carried out using generalized gradient approximation (GGA) + an on-site Coulomb self-interaction correction potential (GGA + U). The magnetic and orbital moments are estimated. The U value was considered to be equal to 6 eV for Co atom. The average equilibrium voltage over a full cycle, of the LiCoBO3 battery is estimated from our FP-LAPW calculations. The capacity of a cell and energy density of LiCoBO3 were calculated. The compound LiCoBO3 is a semiconductor with average intercalation voltage 4.01 V. The voltage difference help promote electrochemical performance, which opens a window for Li-ion battery marketing application.

Prediction of electronic and optical properties for Zn1-xCdxSeyTe1-y quaternary alloys: First-principles study

In the present work, the density functional theory (DFT) was performed for the investigation of the structural, electronic and optical properties of the Zn1-xCdxSeyTe1-y quaternary alloys using the full potential linearized augmented plane wave (FP-LAPW) method. For the calculations of the structural properties we have used the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBEsol). On other hand, the electronic properties have been computed within the local density approximation (LDA) in adding to the Tran-Blaha modified Becker-Johnson (TB-mBJ) approach. Our results indicate that the lattice constant, as well as the bulk modulus and the energy gap for the Zn1-xCdxSeyTe1-y quaternary show almost linear variations on the concentration x (0.125≤x≤0.875). In addition, the simulated band structures for theZn1-xCdxSeyTe1-y quaternary exhibits a direct-gap for all concentrations. Moreover, low bowing parameters are observed. Also, some interesting optical properties such as dielectric constant, refractive index, extinction coefficient, absorption coefficient and reflectivity have been calculated by using the TB-mBJ method. The results of our computations shows that theZn1-xCdxSeyTe1-y quaternary alloy is a promissing candidate for optoelectronic applications. It is noteworthy that the present work is the first theoretical study of the quaternary of interest using the FP-LAPW calculations.

Ferromagnetism induced by calcium vacancies in Ca3BiP anti-perovskite: An ab-initio calculation

We study all possibilities of vacancy that can induce the magnetism in Ca3BiP anti-perovskite using a full-potential linearized-augmented plane-wave calculation within the generalized gradient approximation (PBE-GGA) and a modified version proposed by Becke and Johnson (TB-mBJ) for the exchange-correlation potential. The effects of spin-orbit coupling (SOC) are also considered in this study. We have examined the effect of all cation and/or anion vacancies on the magnetic structure in this system. For Ca3BiP bulk non-magnetic, the calculated band structures and densities of states show a semi-metallic and semi-conductor character obtained by PBE-GGA and TB-mBJ approximations respectively. Without spin-orbit interactions, we find that Ca3-xBiP and Ca3-xBiP1-x relaxed systems have magnetic moments of 2.44701 μB and 3.96894 μB respectively. Both approaches results show that the calcium and phosphorus vacancies are responsible for the magnetism in anti-perovskite Ca3BiP due to the spin-polarization that comes mainly from the valence states of the nearest atoms surrounding these vacancies. In the case of the other studied vacancies, the magnetism was not induced and all materials adopt a metallic character.

Examining the uniform strain effect on elastic, electronic and optical properties of CsPbCl3 through FP-LAPW calculations

We study comprehensively the uniform strain effect on the elastic, electronic and optical properties of the perovskite CsPbCl3 using theoretical calculations based on the Full-Potential Linearized Augmented Plane-Wave (FP-LAPW) method. The Generalized Gradient Approximation (GGA-PBESol) and Tran-Blaha modified Becke-Johnson exchange potential improved by Koller (KmBJ) are adopted to describe the electron exchange-correlation interactions. The compound is elastically stable and ductile. And its mechanical resistance increases with the compressive strain but decreases with the tensile stress. Based on results, CsPbCl3 is a direct semiconductor with band gap of 2.990 eV, which increases when the strain switches nature from compressive to tensile. The optical absorption of CsPbCl3 can be enhanced by applying a compressive strain, and the absorption band can be widen to 620 nm in the visible region with a compressive strain of −5%, making it suitable for photovoltaic applications. Therefore, the strain engineering on CsPbCl3 may be very useful to determine suitable parameters for applications in the optoelectronics industry.

Metallization and positive pressure dependency of bandgap in solid neon.

The metallization of neon remains a controversial problem as there is no consensus in theoretical simulations and no experimental verification. In this work, the insulator-to-metal transition in fcc solid neon at high pressure was revisited with a coupling of the all-electron full-potential linear augmented-plane wave (FP-LAPW) method and the GW correction to avoid the potential unreliability of pseudopotential under high pressure and correct the inaccurate energy gaps caused by local density or generalized gradient approximation of the exchange-correlation. This FP-LAPW + GW calculation predicts that the bandgap closes at a density of 88.3 g/cm3 and a pressure of 208.4 TPa. Moreover, the reported positive pressure dependency of energy gap (increases with increasing density) for solid neon in 1.5-10.0 g/cm3 was confirmed with our FP-LAPW calculations, and the underlying mechanism was first revealed based upon analysis of the charge density distribution and the electron localization function. The results of this research will provide a valuable reference for future high pressure experiments and shed new insight into the planetary interiors.

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.

Electronic structure and magnetic properties of Pr–Co intermetallics: ab initio FP-LAPW calculations and correlation with experiments

First-principle calculations combining density functional theory and the full-potential linearized augmented plane wave (FP-LAPW) method are performed to investigate the electronic and magnetic structure of Pr2Co7 in its two polymorphic forms, (2:7 H) and (2:7 R), for the first time. This type of calculation was also performed for PrCo5 and PrCo2 intermetallics. We have computed the valence density of states separately for spin-up and spin-down states in order to investigate the electronic band structure. This is governed by the strong contribution of the partial DOS of 3d-Co bands compared to the partial DOS of the 4f-Pr bands. Such a high ferromagnetic state is discussed in terms of the strong spin polarization observed in the total DOS. The magnetic moments carried by the Co and Pr atoms located in several sites for all compounds are computed. These results mainly indicate that cobalt atoms make a dominant contribution to the magnetic moments. The notable difference in the atomic moments of Pr and Co atoms between different structural slabs is explained in terms of the magnetic characteristics of the PrCo2 and PrCo5 compounds and the local chemical environments of the Pr and Co atoms in different structural slabs of Pr2Co7. From spin-polarized calculations we have simulated the 3d and 4f band population to estimate the local magnetic moments. These results are in accordance with the magnetic moments calculated using the FP-LAPW method. In addition, the exchange interactions Jij are calculated and used as input for M(T) simulations. Involving the data obtained from the electronic structure calculations, the appropriate Padé Table is applied to simulate the magnetization M(T) and to estimate the mean-field Curie temperature. We report a fairly good agreement between the ab initio calculation of magnetization and Curie temperature with the experimental data.

FP-LAPW calculations of the elastic, electronic and thermoelectric properties of the filled skutterudite CeRu4Sb12

We have investigated the electronic structure, elastic and thermoelectric properties of the filled skutterudite CeRu4Sb12 using the density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method within a framework of the generalized gradient approximation (GGA) approach is used to perform the calculations presented here. The electronic structure calculation suggests an indirect band gap semiconducting nature of the material with energy band gap of 0.08eV. The analysis of the elastic constants at relaxed positions reveals the ductile nature of the sample material with covalent contribution in the inter-atomic bonding. The narrow band gap semiconducting nature with high value of Seebeck coefficient suggests the possibility of the thermoelectric application of the material. The analysis of the thermal transport properties confirms the result obtained from the energy band structure of the material with high thermopower and dimensionless figure of merit 0.19 at room temperature.

Theoretical and experimental investigations of the structural, magnetic, electronic, and electrical properties of olivine LiFePO4

The LiFePO4 and FePO4 compounds were synthesized by coprecipitation method. The X-ray diffraction and magnetic measurements were used to determine the crystal structure and to investigate the magnetic properties, respectively. From theoretical investigation point of view, self-consistent ab initio calculations, based on Density Functional Theory approach and using Full Potential linearized Augmented Plane Wave (FLAPW) method, were performed to investigate both electronic and magnetic properties of the LiFePO4. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Fe plans. Magnetic moments considered to lie along (010) axes are computed. In addition, average equilibrium voltage over a full cycle (Vcell) of the LiFePO4 battery is estimated from our FLAPW calculations. Computed magnetic moments are used as input for the high temperature series expansion (HTSE) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe–Fe and Fe–O–Fe in LiFePO4 are obtained using the mean field theory. The Néel temperature and critical exponent associated with the magnetic susceptibility are obtained employing HTSEs. The obtained inverse magnetic susceptibility is revealed in good accordance with our experimental data.

Electronic structure of Cu2ZnGeSe4 single crystal: Ab initio FP-LAPW calculations and X-ray spectroscopy measurements

High-quality Cu2ZnGeSe4 single crystal has been successfully grown by a solution-fusion method and the crystal structure of the compound is refined within tetragonal kesterite-type (space group 14¯), with the unit cell parameters a=5.6112(1) Å and c=11.0473(3) Å. X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces of the Cu2ZnGeSe4 crystal are measured. Our X-ray photoelectron spectroscopy (XPS) data indicate that the Cu2ZnGeSe4 single crystal surface is very rigid with respect to Ar+ ion-irradiation. The electronic structure of the Cu2ZnGeSe4 compound has been theoretically studied using first principles calculation employing the full potential linearized augmented plane wave (FP-LAPW) method. Calculations of the total and partial densities of states of atoms constituting Cu2ZnGeSe4 reveal that the dominant contributors to the valence band of the compound studied are the Cu 3d states, which contribute mainly at the top of the band, while the central portion of the band is composed mainly from the Cu 3d and Se 4p states in almost equal proportion. Additionally, the present FP-LAPW calculations indicate that the bottom of the valence band is dominated by the Zn 3d states, while the bottom of the conduction band is composed mainly from the unoccupied Ge 4s and Se 4p states. The data of the present FP-LAPW calculations are confirmed by comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the valence Cu d, Zn d, Ge p and Se p states and the XPS valence-band spectrum of the Cu2ZnGeSe4 single crystal.

Single crystal growth and the electronic structure of TlPb2Br5

We report on measurements of the X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces of a TlPb2Br5 single crystal grown by the Bridgman–Stockbarger method. The present X-ray photoelectron spectroscopy results reveal high chemical stability of TlPb2Br5 single crystal surface. Total and partial densities of states of atoms constituting TlPb2Br5 are calculated using the full potential linearized augmented plane wave (FP-LAPW) method. The FP-LAPW data indicate that dominant contributors in the valence band of TlPb2Br5 are the Br 4p-like states: their contributions dominate at the top and in the central portion of the valence band with also significant contributions throughout the whole valence-band region. The bottom of the conduction band is composed mainly of contributions of the unoccupied Pb 6p-like states. In addition, our FP-LAPW calculations reveal that TlPb2Br5 is an indirect-gap material with band gap of 2.92eV.

Angle-resolved photoemission spectroscopy study of BaCo2As2

We use angle-resolved photoemission spectroscopy and full-potential linearized augmented-plane-wave (FP-LAPW) calculations to study the electronic structure of BaCo${}_{2}$As${}_{2}$. The Fermi surface (FS) maps and the corresponding band dispersion data (at 90 and 200 K) reveal a small electron pocket at the center and a large electron pocket at the corner of the Brillouin zone. Therefore the nesting between electron and hole FS pockets is absent in this compound, in contrast to the parent compounds of FeAs-based high-$T$${}_{\mathrm{c}}$ superconductors. The electron pockets at the center of the zone are surrounded by two sets of four smaller electron pockets. The electronic structure at about 500 meV binding energy is very similar to features at the chemical potential in BaFe${}_{2}$As${}_{2}$. This indicates that complete substitution of Co for Fe causes a nearly rigid shift in the chemical potential by adding two electrons per formula unit at higher binding energies. However at lower binding energies $\ensuremath{\sim}$270 meV, the electron pocket at the center of the zone is absent, unlike in the Co-substituted Fe-based materials. This demonstrates that the rigid band picture is valid only at higher binding energies and breaks down closer to the chemical potential in BaCo${}_{2}$As${}_{2}$. We also observed the presence of a flat band near the Fermi energy that may have consequences for transport and thermodynamical properties. The experimental FS topology as well as band dispersion data are in reasonable agreement with the FP-LAPW calculations.

Electronic properties of ZnWO4 based on ab initio FP-LAPW band-structure calculations and X-ray spectroscopy data

Total and partial densities of states of the atoms constituting zinc tungstate, ZnWO4, have been calculated using the ab initio full potential linearized augmented plane wave (FP-LAPW) method. The theoretical data reveal that main contributors in the valence band of ZnWO4 are the Zn 3d-, W 5d- and O 2p-like states: the Zn 3d- and W 5d-like states contribute mainly at the bottom, whilst the O 2p-like states at the top of the valence band, with also significant portions of contributions of the above states throughout the whole valence-band region of the tungstate under study. In addition, data of our band-structure FP-LAPW calculations indicate that the conduction band of ZnWO4 is dominated by contributions of the W 5d-like states. To verify the theoretical findings, high-quality inclusion-free ZnWO4 single crystals were specially grown along the [010] direction for the present experimental studies employing the low thermal gradient Czochralski technique. It has been established that, comparison on a common energy scale of the X-ray photoelectron valence-band spectrum and the X-ray emission bands representing the energy distribution of mainly the Zn 3d-, W 5d- and O 2p-like states of ZnWO4 confirm experimentally the present FP-LAPW theoretical data regarding the occupations of the valence band of zinc tungstate.

Electronic structure of the high-temperature tetragonal Tl3PbBr5 phase

We report on calculations of total and partial densities of states of atoms constituting the high-temperature (HT) tetragonal Tl3PbBr5 phase (space group P41) using the full potential linearized augmented plane wave (FP-LAPW) method. Our theoretical data reveal that the tetragonal HT-Tl3PbBr5 phase is an indirect-gap material with band gap of 2.26 eV. In addition, the FP-LAPW calculations render that dominant contributors in the valence-band region of HT-Tl3PbBr5 are the Br 4p-like states, which contribute mainly into the top and the central portion of the valence band with also significant contributions throughout the whole valence-band region. The main contributors to the bottom of the valence band of the HT-Tl3PbBr5 phase are the Tl 6s-like states, whilst the unoccupied Pb 6p-like states dominate at the bottom of the conduction band. The X-ray photoelectron core-level and valence-band spectra for the HT-Tl3PbBr5 phase have been measured and compared with those of previously studied the low-temperature orthorhombic Tl3PbBr5 phase.

Ab initio study on structural stability of uranium carbide

First principles calculations have been performed using plane wave pseudopotential and full potential linearized augmented plane wave (FP-LAPW) methods to analyze structural, elastic and dynamic stability of UC under hydrostatic compression. Our calculations within pseudopotential method suggest that the rocksalt (B1) structure will transform to body centered orthorhombic (bco) structure at ∼21.5GPa. The FP-LAPW calculations put this transition at 23GPa. The transition pressures determined from our calculations though agree reasonably with the experimental value of 27GPa, the high pressure bco structure suggested by theory differs slightly from the experimentally reported pseudo bco phase. The elastic stability analysis of B1 phase suggests that the B1 to bco transition is driven by the failure of C44 modulus. This finding is further substantiated by the lattice dynamic calculations which demonstrate that the B1 phase becomes dynamically unstable around the transition pressure and the instability is of long wavelength nature.

First-principles FP-LAPW calculations and X-ray spectroscopy studies of the electronic structure of Zr3V3O and Zr3V3O0.6 oxides

Electronic properties of Zr3V3O oxide, a very promising hydrogen-storage material, were studied both from theoretical and experimental points of view employing the full potential linearized augmented plane wave (FP-LAPW) method as well as X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). Total and partial densities of states of the constituting atoms of Zr3V3O have been derived from the FP-LAPW calculations. These data indicate that, the O 2p-like states are the dominant contributors in the bottom of the valence band, whilst the top of the valence band and the bottom of the conduction band of Zr3V3O are dominated by contributions of the V2 3d-like states, with slightly smaller contributions of the V1 3d-like states as well. Significant contributions of the Zr 4d-like states throughout the whole valence-band region and near the bottom of the conduction band are also characteristic of the electronic structure of Zr3V3O. The XPS valence-band spectra and the XES Zr Lβ2,15, V Lα and O Kα bands have been derived and compared on a common energy scale for Zr3V3O and Zr3V3O0.6 oxides. This comparison of the experimental spectra was found to be in excellent agreement with the results of the FP-LAPW calculations. In addition, the XPS Zr 3d, V 2p and O 1s core-level binding energies have been measured for Zr3V3O and Zr3V3O0.6 oxides.

One-dimensional ballistic transport with FLAPW Wannier functions

We present an implementation of the ballistic Landauer-B\"uttiker transport scheme in one-dimensional systems based on density functional theory calculations within the full-potential linearized augmented plane-wave (FLAPW) method. In order to calculate the conductance within the Green's function method, we map the electronic structure from the extended states of the FLAPW calculation to Wannier functions, which constitute a minimal localized basis set. Our approach benefits from the high accuracy of the underlying FLAPW calculations, allowing us to address the complex interplay of structure, magnetism, and spin-orbit coupling and is ideally suited to study spin-dependent electronic transport in one-dimensional magnetic nanostructures. To illustrate our approach, we study ballistic electron transport in nonmagnetic Pt monowires with a single stretched bond including spin-orbit coupling, and in ferromagnetic Co monowires with different collinear magnetic alignment of the electrodes with the purpose of analyzing the magnetoresistance when going from tunneling to the contact regime. We further investigate spin-orbit scattering due to an impurity atom. We consider two configurations: a Co atom in a Pt monowire and vice versa. In both cases, the spin-orbit induced band mixing leads to a change of the conductance upon switching the magnetization direction from along the chain axis to perpendicular to it. The main contribution stems from ballistic spin scattering for the magnetic Co impurity in the nonmagnetic Pt monowire, and for the Pt scatterer in the magnetic Co monowire from the band formed from states with ${d}_{xy}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital symmetry. We quantify this effect by calculating the ballistic anisotropic magnetoresistance, which displays values up to as much as 7$%$ for ballistic spin scattering and gigantic values of around 100$%$ for the Pt impurity in the Co wire. In addition, we show that the presence of a scatterer can reduce as well as increase the ballistic anisotropic magnetoresistance.

Structure of the dense amorphous carbon phase synthesized in a mixture with diamond as a result of shock compression of carbon black

Soft X-ray emission and absorption spectroscopy methods were used in the present work to study experimentally the electronic structure of the dense amorphous carbon phase synthesized in a mixture with diamond as a result of shock compression of carbon black. The X-ray emission C Kα bands, representing the energy distribution of the C 2p-like states, have been recorded for the amorphous carbon phase and, for comparison, for diamond, lonsdaleite, graphite, and carbon black. For the amorphous carbon phase, diamond and lonsdaleite the spectra of quantum yields of the X-ray photoeffect in the area of the C K absorption edge have been recorded as well. Total and partial densities of states of the carbon H-6 and bct-4 phases, diamond and lonsdaleite have been calculated using the first-principles self-consistent full potential linearized augmented plane wave (FP-LAPW) method. Comparison on a common energy scale of the X-ray emission C Kα bands and C K quantum yields of the dense amorphous carbon phase as well as the theoretical curves of partial C 2p-like states of the carbon H-6 and bct-4 phases reveals that, the electronic structure of the amorphous carbon phase under consideration is well described by that of the carbon bct-4 phase. The experimental X-ray emission and absorption spectroscopy data indicate that the amorphous carbon phase studied is metallic, being in agreement with the results of the theoretical FP-LAPW calculations.

Vacancy defects in strontium titanate: Ab initio calculation

A full-potential linearized-augmented plane-wave calculation was used to study structural and electronic properties of defected SrTiO 3 with two concentrations of oxygen vacancies. These properties were found to remarkably depend on the oxygen vacancy concentration. The defect states associated with oxygen vacancies are identified within the energy gap. The ground state properties, equilibrium lattice constants, bulk moduli, the formation energy, densities of electron states, band structures and charge density are determined and discussed for this compound. It is found that an oxygen vacancy creates more localized in-gap states. With increasing oxygen deficiency, the electrons left behind by oxygen removal not only localize on Sr (Ti) 3 d orbitals but also on the vacancy sites. Model structures of 2 × 2 × n ( n = 1, 2, 3 and 4) supercells are used.

Electronic structure of FeWO 4 and CoWO 4 tungstates: First-principles FP-LAPW calculations and X-ray spectroscopy studies

Total and partial densities of states of the constituent atoms of iron tungstate, FeWO 4, and cobalt tungstate, CoWO 4, have been calculated using the first-principles self-consistent full potential linearized augmented plane wave (FP-LAPW) method. The results obtained reveal that the O 2p-like states are the dominant contributors into the valence band of the tungstates under consideration, whilst the bottom of the conduction band of FeWO 4 and CoWO 4 is dominated by contributions of the empty Fe 3d- and Co 3d-like states, respectively. The FP-LAPW data indicate that the O 2p-like states contribute mainly into the top of the valence band, with also significant contributions throughout the whole valence-band region, of FeWO 4 and CoWO 4 compounds. Other significant contributors into the valence-band region are the Fe 3d- and W 5d-like states in FeWO 4 and the Co 3d- and W 5d-like states in CoWO 4. All the above d-like states contribute throughout the whole valence-band region of the tungstates under consideration, however maximum contributions of the W 5d-like states occur in the lower, whilst the Fe (Co) 3d-like states in the upper portions of the valence band, respectively. To verify the above FP-LAPW data, the X-ray emission bands representing the energy distributions of mainly the valence O p-, Fe (Co) d-, Fe (Co) p- and W d-like states were measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum of the corresponding tungstate. The experimental data were found to be in good agreement with the theoretical FP-LAPW results for the electronic structure of FeWO 4 and CoWO 4 compounds.