Total Electronic Densities Of States Research Articles

Theoretical modeling of the electronic structure and Fermi surfaces of Gd4Sb3 and GdSb2 compounds

Our theoretical modeling of the electronic structure in the intermetallic Gd4Sb3 and GdSb2 compounds has been done in the framework of density functional theory accounting for spin-orbit coupling. It revealed the metallic character of the summed total density of electronic states for both materials. The complicated Fermi surfaces were found in the half-metallic Gd4Sb3 compound which corresponds to the band structure. The GdSb2 material is obtained to be a bad metal with the low density of states near the Fermi energy, the Fermi surfaces of GdSb2 are found to have the cylindrical shape.

Spectral and quantum mechanical investigation of calcium apatites isomorphically substituted in the anionic sublattice

The evolution of the valence band, the charge states of atoms, and the optical and vibrational spectra in Ca10(PO4)x(VO4)y(AsO4)z(OH)2 (x + y + z = 6) compound with three different types of oxygen tetrahedra have been studied by XPS, IR, and optical spectroscopy with the use of quantum mechanical calculation methods in the DFT approximation. It is shown that the occupied part of the valence band of compounds with three different types of tetrahedra has a pronounced band character with varying lengths of individual subbands. Two structural regions separated by energy are observed: the valence band's upper part and the valence band's lower part (subvalent states). The structure of the valence band's middle part, the region of valence states with energies from ∼ 13.0–19.0 eV, is weakly expressed. The sublattice of oxygen tetrahedra is decisive in forming the shape and the main features of the total density of electronic states of the compounds under study. The vibrations anharmonicity in the crystal lattice of such compounds can vary depending on the concentration of tetrahedra of a specific type. Such changes are local, and with the help of directed substitutions, it is possible to create the required spatial distribution of the anharmonic component over the crystal.The design of the calcium apatites structure by the method of isomorphic substitutions of (XO4) tetrahedra with tetrahedra of various types and with different ratios makes it possible to control the energy band gap width.

Experimental and theoretical studies of synthesized Bi2NiCrO6 double perovskite material

• Bi 2 NiCrO 6 is synthesized by the sol-gel method. • Bi 2 NiCrO 6 shows a cubic structure with an Fm3m space group. • Bi 2 NiCrO 6 exhibits metallic and ferromagnetic behaviors and its magnetic moment is 1.17μB. • Bi 2 NiCrO 6 is a good candidate for spintronic application. In this work, the experimental and theoretical studies of Bi 2 NiCrO 6 double perovskite material have been performed. The synthesis of Bi 2 NiCrO 6 is made by sol-gel method. The X-ray diffraction (XRD) characterisation of the material reveals that the double perovskite adopts a cubic structure (a=7.75 Å) with Fm3m space group. Based on the Density Functional Theory (DFT) with spin polarized calculations, the electronic and magnetic properties have been investigated. From the total electronic density of states and the electronic band structure analysis, it is found that Bi 2 NiCrO 6 exhibits a metallic behavior. It is also found that the studied compound is ferromagnetic material with a total magnetic moment 1.17 μ B . The results show that Bi 2 NiCrO 6 material is a good candidate for using in devices that requires multifunctional operations including spintronic.

Electronic, Structural, Mechanical, and Thermodynamic Properties of CoYSb (Y = Cr, Mo, W) Half-Heusler Compounds as Potential Spintronic Materials

We used density functional theory (DFT) calculations to investigate the structural, electronic, magnetic, mechanical, and thermodynamic properties of CoYSb (Y = Cr, Mo and W) compounds. These are XYZ type half-Heusler alloys, which also exist in the face centred cubic MgAgAs-type structure and conform to F4¯3m space group. We computed these properties in three different atomic arrangements known as Type-I, Type-II, and Type-III phases. In all these phases, the alloys were found to be in the ferromagnetic state. Furthermore, the calculated electronic band structure and the total electronic density of states indicated a metallic behavior in CoWSb, nearly half-metallic behavior in CoMoSb, and half-metallic behavior in CoCrSb, with a minority-spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behavior of these alloys in their stable phase. Finally, due to its high Debye temperature value, CoCrSb shows stronger covalent bonding than CoMoSb and CoWSb, respectively.

Ab initio calculations of electronic properties and charge transfer in Zn-=SUB=-1-x-=/SUB=-Cu-=SUB=-x-=/SUB=-O with wurtzite structure

The results of studying the electronic structure and the influence of the local environment of the copper impurity on the properties and magnetic moment in supercells in Zn1-xCuxO are presented. DFT calculations were carried out in the local electron density (LDA) and generalized gradient approximation (GGA). The band structure of in Zn1-xCuxO was calculated taking into account the correction for spin polarization and the strong electronic interaction. DFT LSDA + U and SGGA + U (U is the Coulomb interaction) calculations made it possible to take into account the contributions of the 3d shells of the Zn and Cu cations to the band spectrum of in Zn1-xCuxO. The introduction of copper into the ZnO lattice leads to a change in the impurity and valence bands of in Zn1-xCuxO. In this case, the bottom of the in Zn1-xCuxO conduction band shifts towards low energies. The total density of electronic states of in Zn1-xCuxO near the Fermi level is mainly determined by the 3d states of Zn and Cu and the 2p state of oxygen. ZnO doped with copper acquires a magnetic moment. The introduction of a vacancy into a supercell in Zn1-xCuxO noticeably changes the local magnetic moment. As the copper concentration in Zn1-xCuxO (x=0, 0.01, and 0.02) increases, the conductivity of the samples in both constant and alternating current increased, and the activation energy of conduction decreased. Keywords: ZnO, copper doping, density functional theory, band calculations, electronic structure, localized magnetic moment, defect formation energies, Zn1-xCuxO, charge transfer, parameters of localized states.

Two-dimensional quantum dots for highly efficient heterojunction solar cells

The electronic and optical properties of finite silicene, graphene, and arsenene heterostructures are investigated using first principles calculations. The optoelectronic properties of these structures are precisely controlled, by chemical functionalization, shape, and size, to produce suitable donor energy gap and minimal conduction band offset that enable the construction of efficient heterojunction solar cells. Heterojunctions with only Van der Waals interactions between layers have been achieved in functionalized silicene/graphene and arsenene/graphene. The distribution of the highest occupied/lowest unoccupied molecular orbital on donor/acceptor layer in addition to the contribution of each layer into the total electronic density of states insure that the only interlayer interaction is the van der Waals one and charge separation is attained. The heterojunctions have donors’ energy gaps ranging from 1.2 to 1.8 eV which in conjunction with the very low conduction band offset ∼ 0.002 eV enable the building of type-II solar cells with extremely high power conversion efficiency up to 23.34%. The prominent low energy optical excitations are mainly contributed by a transition from donor molecular orbitals to acceptor ones. Therefore, functionalized 2D heterojunctions are excellent candidates for building ultrathin, stable, and low-cost efficient solar cells.

Structural, vibrational and electronic properties of D03 FeNi3

The Fe-Ni invar alloys attract the great interest of researchers due to their anomalously low coefficient of thermal expansion for Fe-rich compositions and numerous technological and practical applications. The structural, vibrational and electronic properties of D03 FeNi3 studied using the first-principles plane wave self-consistent method with the Ultrasoft pseudopotential scheme under the framework of DFT. Calculated equilibrium lattice constant and isothermal bulk modulus for D03 FeNi3 presented with the other available results. Existence of imaginary phonon frequencies in the phonon dispersion curves of D03 FeNi3 suggest the dynamical instability of it. Significant contribution of d-electrons to the total electronic density of states is in agreement with the previously reported work. Electronic charge density plots for D03 FeNi3 predict weak metallic bonding between Fe and Ni compared to between Fe-Fe metal atoms. Fermi surface topology exhibit electron and/or hole character at different high symmetrical points of the Brillouin zone based on the crossing of bands at EF in the electronic band structure. Conclusions based on the phonon dispersion curves, phonon density of states, electronic band structure along with the total and projected density of states, electronic charge density and Fermi surface are summarized.

Structural, magnetic and electronic properties of FeRhxPd1-x compounds: Ab initio study

In this paper, structural, magnetic and electronic properties of FeRhxPd1-x (x = 0, 0.125, and 0.25) were investigated by first principles calculations. The two types of crystal structures CuAu-type and CsCl-type are considered. The lattice parameters, energy, partial and total magnetic moments, formation energy, total density of electronic states and the projected density of states for t2g and eg orbitals for Fe–Rh–Pd with different magnetic ordering are calculated.

First principles study on new half-metallic ferromagnetic ternary zinc-based sulfide and telluride (Zn3VS4 and Zn3VTe4)

In this resear, we have investigated electronic and magnetic behavior and also some mechanical properties of ternary zinc-based chalcogenides Zn3VCh4 (Ch = S and Te) conform to space group with 215 space number, which have simple cubic (SC) crystal structure, by spin-polarized Generalized Gradient Approximation (GGA) within Density Functional Theory (DFT). To make extensive study within ab initio methods, after the optimization process to get optimal structural parameters in most suitable magnetic phase, the electronic band structures with the total density of electronic states and second order elastic constants to predict some thermal and elastic features have been calculated. The calculated negative formation enthalpy values indicate that, our materials are thermodynamically stable and structurally synthesizable. The observed minority (down) band gaps in the calculated electronic band structures, Eg = 2.62 eV for Zn3VS4 and Eg = 1.75 eV for Zn3VTe4, show that our crystal systems have half-metallic character. Also, the calculated elastic constants prove that our compounds are mechanically stable due to satisfy the Born-Huang criteria. Moreover, the anisotropic elastic properties have been visualized in two-dimensional (2D) and three-dimensional (3D) surfaces for Young’s modulus, linear compressibility, shear modulus and Poisson’s ratio as well as with the calculation of the anisotropic factors.

КРЕМНИЙ-НИОБИЕВЫЕ БЛОКИ ДЛЯ КОНСТРУИРОВАНИЯ НАНОСТРУКТУРИРОВАННЫХ МАТЕРИАЛОВ

Представлены результаты компьютерного моделирования пространственной структуры анионных кремний-ниобиевых кластеров из 10, 12, 14 и 16 атомов кремния. Для каждого кластера представлен ряд стабильных изомеров с качественно различной структурой, которые могут служить элементарными блоками для построения более крупных наноструктурированных объектов – нанопроволок, нанопроводов, нанокристаллов.
 Для представленных расчетов были использованы вычислительные ресурсы Суперкомпьютерного центра Воронежского государственного университета.

Investigation of the electronic structure of tetragonal B3N3 under pressure

In this paper, we perform self-consistent field relaxation and electronic structure calculations of tetragonal B3N3 based on density functional theory, using LDA pseudopotential in the pressure range between − 30 and + 160 GPa. Although metallic B3N3 has a honeycomb structure, according to the electronic band structure, it has bulk properties (not layered) with effective mass non-interacting electron gas behavior near Fermi level (not Dirac massless) and a small anisotropy, about 0.56 in effective mass in the direction of MA relative to XM. Electronic calculations of the B3N3 under pressure show that increasing positive pressure causes the decrease of Fermi energy and total electronic density of states at Fermi level, due to the ionic bonding nature in the B3N3. The Fermi energy increases a little in pressure ranges of about + 100 to + 160 GPa. According to performed projected density of states calculations of the B3N3 under pressure, which p orbitals of boron and nitrogen atoms with three sp2 hybridized bonding have the most contribution in the electronic states at Fermi level, that have spatial distribution perpendicular to honeycomb planes in pressure range of − 30 to + 160 GPa, like p z orbitals in graphene. In overall, the contribution of the p orbitals of nitrogen atoms is greater than similar p orbitals of boron atoms. Accordingly, the orbitals of nitrogen and boron atoms with higher order, sp3 hybridized bonding have negligible electronic contribution at Fermi level in the all pressure range.

An ab initio study on the structural, electronic and mechanical properties of quaternary full-Heusler alloys FeMnCrSn and FeMnCrSb

ABSTRACT The quaternary full Heusler alloys FeMnCrSn and FeMnCrSb, which have face-centred cubic (FCC) crystal structure and conform to space group with 216 space number, have been investigated using Generalised Gradient Approximation (GGA) in the Density Functional Theory (DFT) as implemented in VASP (Vienna Ab initio Simulation Package) software. These alloys are considered in ferromagnetic (FM) order. After the investigation of structural stability of these alloys, their mechanical and thermal properties and also electronic band structures have been examined. The calculated spin-polarised electronic band structures and total electronic density of states (DOS) within GGA approximation show that these alloys can exhibit both metallic and half-metallic characters in different structural phases. The calculated formation enthalpies and the plotted energy-volume graphs show that Type-III phase is most stable structural phase for these materials. Also, FeMnCrSb alloy in Type-I/Type-III phases and FeMnCrSn alloy in Type-III phase show half-metallic behaviour with integer total magnetic moments almost 2 and 1 μ B per formula unit, respectively, since there are band gaps observed in spin-down states, whereas they have metallic behaviour in majority bands. Other structural phases of both systems are also metallic. Moreover, the calculated elastic constants and the estimated anisotropy shear factors indicate that these materials are stable mechanically in all of three phases except FeMnCrSn in Type-I phase that does not satisfy Born stability criteria in this phase and have high anisotropic behaviour.

The Investigation DO3-type Fe3M (M=Al, Ga, Si and Ge) Full-Heusler Alloys Within First Principles Study

Full-Heusler Fe 3 M (M=Al, Ga, Si and Ge) alloys whose crystal structure is DO 3 -type disordered structure which conforms to Fm 3 m space group, have been investigated by using Local Spin Density Approximation ( LSDA) and Generalized Gradient Spin Approximation ( GGSA) i n the Density Functional Theory (DFT) as implemented in VASP ( Vienna Ab initio Simulation Package) software . After t he examination of ground states of our materials in DO 3 -type structure , their full structural, mechanical properties and electronic band structures have been investigated and made comparison between LSDA and GGSA . The calculated electronic band structures and total electronic density of states (DOS) within both of two approximation show that these alloys have metallic behavior. T he calculated elastic constants and estimated mechanical properties depended on these constants indicate that these alloys are stable mechanically and have anisotropic behavior .

First-principles study on Jahn-Teller effect in Cr monolayer film

Computational physics has been used in many scientific research fields, in which first-principles calculation based on density functional theory has made brilliant achievements. Unlike three-dimensional materials, low-dimensional materials present fantastic physical effect, due to the reduction of material dimensions. With the rapid development of two-dimensional materials, people have a more in-depth understanding of them. Requirements for high performance of two-dimensional materials are raised for potential applications, so the exploration of some effects affecting the stability of two-dimensional materials becomes more and more important. Based on the pioneers' work, Jahn-Teller effect is found to have a certain influence on the stabilities of two-dimensional structure of some elements. In the present paper, we explain the stable structure of Cr monolayer film through theoretical calculation, providing a guidance for experimental synthesis. Using first-principles calculation, we study a series of two-dimensional structures (rectangular, square, hexagonal, oblique and centered rectangular) of Cr monolayer film, focusing on the structural stability and electronic properties. Firstly, the equilibrium lattice constant and cohesive energy of each structure are calculated. Then, the bond angle and lattice constant dependence of the total energy are analyzed in detail. Finally, we investigate the energy band structures, total electronic densities of states, charge densities and electron occupation numbers of orbitals. The results show that low-symmetry oblique and centered rectangular lattice are stable in the two-dimensional system of Cr, while high-symmetry square and hexagonal lattices are not stable and the adhesive energy of the rectangular lattices is very small. Two stable structures of Cr monolayer sheet are formed due to hexagonal structure distortion. The hexagonal structure can shape into a centered rectangular structure with the increase of bond angle, while it changes into an oblique structure with the decrease of bond angle. Because of Jahn-Teller effect, the degenerate energy level spontaneously splits. Then the structure deforms into two reduced-symmetry structures, resulting in a stable system. Therefore, we can infer that the Jahn-Teller effect plays a crucial role in the structural stability of monolayer sheet.

An ab initio study on the investigation of structural, electronic, mechanical and lattice dynamical properties of the M2AX type MAX phases Sc2AlB0.5C0.5, Sc2AlB0.5N0.5 and Sc2AlC0.5N0.5 compounds

The hypothetical Sc2AlB0.5C0.5, Sc2AlB0.5N0.5 and Sc2AlC0.5N0.5 compounds are M2AX type MAX phases referred to as #211 and have hexagonal crystal structure which conforms to P63/mmc space group. These compounds have been investigated by using generalized gradient approximation in the Density Functional Theory and plane-wave pseudopotential method. After the optimization process of the compounds, their structural, electronic, mechanical, and lattice dynamical properties have been examined in detail. The calculated electronic band structure and the total electronic density of states indicated that all of our compounds have metallic behavior. The estimated elastic constants show that they are stable and have anisotropic character mechanically. Moreover, Sc2AlB0.5C0.5 and Sc2AlB0.5N0.5 are ductile, while Sc2AlC0.5N0.5 is brittle. Also, the obtained phonon dispersion curves indicate that Sc2AlC0.5N0.5 is stable, whereas Sc2AlB0.5C0.5 and Sc2AlB0.5N0.5 compounds are dynamically unstable with imaginary vibrational modes.

A First-Principles Study of Hydrogen Diffusivity and Dissociation on δ-Pu (100) and (111) Surfaces

The diffusivity and chemical reactivity of hydrogen on the δ-Pu (100) and (111) surfaces has been studied with density functional theory using both spin-polarization and spin–orbit coupling calculations. Comparison of the total electronic density of states and atomic hydrogen diffusion energies indicates that spin-polarization yields accurate results, with spin–orbit coupling yielding slightly smaller barriers to hopping between adsorption sites. On the (100) surface, both sets of calculations indicate that the dissociation reaction for molecular hydrogen is highly active at ambient conditions and results in the hydrogen ions bonded within the Pu surface, similar to hydride formation. In contrast, calculations on the (111) surface indicate a lower barrier for dissociation without the formation of the hydride-like end product. Our results help quantify the effect of spin–orbit coupling on hydrogen surface chemistry on δ-Pu. In addition, we observe that the degree of resulting corrosion could depend on the ...

The investigation of electronic, magnetic, mechanical, and lattice dynamical properties of PdMX (M = Cr, Fe and X = Si and Ge) ferromagnetic half-Heusler metallics: an ab initio study

PdMX (M = Cr, Fe and X = Si, Ge) half-Heusler alloys, have been investigated in cubic C1b crystal structure which conforms to space group by using local spin density approximation (LSDA) within the density functional theory (DFT). Firstly, for all materials, the most stable structural phase, which is type-II phase, has been determined. Then, all materials have been considered in ferromagnetic (FM), paramagnetic (PM) and antiferromagnetic (AFM) orders in the most stable type-II structure. The estimated Curie temperatures by using energy differences between FM and PM phases in mean field approximation have been found to be noticeably higher than the room temperature. After the determination of the most stable magnetic phase, their full structural, mechanical, electronic, and lattice dynamical properties have been studied in the most stable magnetic and structural phase. The calculated electronic band structure and total electronic density of states (DOS) have showed that there is no band gap revealing metallic behavior. The estimated elastic constants and calculated phonon dispersion curves have confirmed the stability of FM phase, both mechanically and dynamically.

The investigation of electronic, mechanical and lattice dynamical properties of PdCoX (X = Si and Ge) half-Heusler metallics in α, β and γ structural phases: an ab initio study

PdCoX (X = Si and Ge) alloys which are XYZ type half-Heusler alloys and also have face centred cubic MgAgAs-type structure which conforms to space group, have been investigated in different atomic arrangements which are called α, β and γ phases, using local spin density approximation in the density functional theory as implemented in VASP (Vienna Ab Initio Simulation Package) software. Both of the alloys are considered in ferromagnetic order. After the investigation of stable structural phase for these alloys, their full structural, electronic, magnetic, mechanical, and dynamical properties have been examined in this structural phase. The calculated electronic band structure and the total electronic density of states of our alloys indicated metallic behaviour. The estimated elastic constants show that these are stable and show anisotropic behaviour mechanically in β and γ phases. Also, the calculated phonon dispersion curves show that PdCoX (X = Si and Ge) alloys are stable dynamically in the same structural phases.

The effects of strong correlations on the band structure of Ag8SnSe6 argyrodite

The electronic energy band spectra, as well as partial and total density of electronic states of the crystal argyrodite Ag$_{8}$SnSe$_{6}$ have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The one-electron energies have been evaluated using two functionals for exchange-correlation energy. The first one is the generalized gradient approximation (GGA) approach. The second one is the hybrid functional PBE0 composed of the semilocal GGA part and Hartree-Fock exact exchange non-local energy for strongly correlated $4d$ electrons of Ag atom. The second approach eliminates the Coulomb self-interaction of the Ag $4d$ electrons. This leads to a significant restructuring of the energy bands in the filled valence part and to an improved location of the Ag $4d$-states on the energy scale, and the resulting value of the band gap is well compared with experiment. The effects of strong correlation on the electronic structure of the crystal argyrodite are considered here for the first time.

First-principles study of a sodium borosilicate glass-former. II. The glass state

We use ab initio simulations to investigate the properties of a sodium borosilicate glass of composition ${3\mathrm{Na}}_{2}\mathrm{O}\ensuremath{-}{\mathrm{B}}_{2}{\mathrm{O}}_{3}\ensuremath{-}6{\mathrm{SiO}}_{2}$. We find that the broadening of the first peak in the radial distribution functions ${g}_{\mathrm{BO}}(r)$ and ${g}_{\mathrm{BNa}}(r)$ is due to the presence of trigonal and tetrahedral boron units as well as to nonbridging oxygen atoms connected to ${\mathrm{BO}}_{3}$ units. In agreement with experimental results, we find that the $^{[3]}\mathrm{B}$ units involve a significant number of nonbridging oxygens, whereas the vast majority of $^{[4]}\mathrm{B}$ have only bridging oxygens. We determine the three-dimensional distribution of the Na atoms around the $^{[3]}\mathrm{B}$ and $^{[4]}\mathrm{B}$ units and use this information to explain why the sodium atoms associated with the latter share more oxygen atoms with the central boron atoms than the former units. From the distribution of the electrons we calculate the total electronic density of states, as well its decomposition into angular momentum contributions. The vibrational density of states shows at high frequencies a band that originates from the motion of the boron atoms. We find that the $^{[3]}\mathrm{B}$ and $^{[4]}\mathrm{B}$ units give rise to well-defined features in the spectrum, which thus can be used to estimate the concentration of these structural entities. The contribution of $^{[3]}\mathrm{B}$ can be decomposed further into symmetric and asymmetric parts that can also be easily identified in the spectrum. Furthermore, it is found that certain features in the spectrum can be used to obtain information on the type of atom that is the second-nearest neighbor of a boron in the $^{[4]}\mathrm{B}$ unit. We calculate the average Born charges on the bridging and nonbridging oxygen atoms and show that these depend linearly on the angle between the two bonds and the distance from the connected cation, respectively. Finally, we have determined the frequency dependence of the dielectric function, as well as the absorption spectra. The latter is in good quantitative agreement with the experimental data.