Partial Densities Of Electronic States Research Articles

First principles calculations of the stability of the T2 and D88 phases in the V–Si–B system

The crystal and electronic structures of D8l-V5SiB2 and D88-V5Si3B ternary compounds have been investigated by means of first principle calculations. The calculated structural parameters are in very good agreement with the experimental data. The calculated values of the enthalpies of formation at T = 0 K of the D8l-V5SiB2 and D88-V5Si3B ternary compounds are −67.1 and −62.1 kJ/mol of atoms respectively. The total and partial electronic densities of states show a strong hybridization between the B p states and V d states. The defect enthalpies of formation as well as the mixing enthalpies have been computed. These data are essential for the modeling of the D8l and D88 phases in the V–Si–B ternary system. A partial V–VSi2–VB isothermal section at 298 K is proposed.

First-principle study of the transition-metal adatoms on B-doped vacancy-defected graphene

The energetic, electronic, and magnetic properties of transition metal (TM) atoms absorbed on modified graphene, including B-dopant, vacancy, and combination of these two, were theoretically investigated using the density functional theory (DFT) method. It was found that the adsorption of TM atoms (V, Mn, Fe and Ni) was significantly enhanced by the presence of vacancy sites. Furthermore, the introduction of B-dopant affected the adsorption process of TM atoms and the band structure of graphene. The results of partial electronic density of states (PDOS) indicated that the influence by B-dopant was due to the interaction between the 2p orbital of B atoms and 3d orbital of TM atoms. Interestingly, the strong hybridization contributed by B-2p and C-2p at vacancy sites enlarged the adsorption energies of TM-adatoms. It is expected that the results could provide useful information to explore application of graphene as spintronic and electronic devices.

Structure of the fluorine states in cadmium molybdate host studied by the electronic band structure calculations of CdMoO4, CdMoO4:F and CdMoO3F2 crystals

The electronic structures of CdMoO4, CdMoO3F2 and the fluorine-doped CdMoO4:F crystals are calculated by the Full-Potential Linear Augmented Plane Wave method. The energy dispersion curves, partial densities of electronic states and spatial distributions of electronic densities are calculated and analyzed in comparison with published experimental data. Relaxation of the crystal structure around the FO impurity in cadmium molybdate is revealed in geometry-optimization calculations carried out for CdMoO4:F. It is found that CdMoO3F2 crystal is as a direct-gap material. The Cd d, F p and O p states electronic states form the top of the Valence band and mainly Mo d states form the bottom of the Conduction band of CdMoO3F2 and all these states are involved into the lowest-energy band-to-band electronic transitions. The low-energy shift of the main bands in intrinsic luminescence emission and excitation spectra of CdMoO3F2 with respect to CdMoO4 may be a consequence of the lower Eg value of the oxyfluoromolybdate. Calculations suggest more complex structure of the luminescence centers in CdMoO3F2 in comparison with CdMoO4.

Tuning electrochemical potential of LiCoO2 with cation substitution: first-principles predictions and electronic origin

With a goal to improve the performance of LiCoO2 as a cathode material in Li-ion batteries, we simulate substitution of various elements (X = Be, Mg, Al, Ga, Si and Ti) for Co using first-principles density functional theory and predict changes in its electrochemical potential. While the electrochemical potential of LiCoO2 is enhanced with substitution of Be, Mg, Al and Ga for Co, an opposite effect is predicted of Si and Ti substitution. We determine the electronic origin of these changes in electrochemical potential using (a) Bader method of topological analysis of charge density, (b) partial density of electronic states to estimate oxidation states of metal and oxygen, and charge re-distribution upon lithiation. We find that the distribution of electronic charge donated by Li is influenced by the nature of the X–O bond. A larger electron transfer to O (in XO6 octahedron) upon lithiation leads to stronger Li intercalation and thereby higher electrochemical voltage. Our findings provide a platform for a rational design of cathode materials in Li batteries with enhanced voltage.

Electronic properties and fermi surface for new Fe-free layered pnictide-oxide superconductor BaTi2Bi2O from first principles

Very recently, as an important step in the development of layered Fe-free pnictide-oxide superconductors, the new phase BaTi2Bi2O was discovered which has the highest TC (about 4.6 K) among all related non-doped systems. In this Letter, we report for the first time the electronic bands, Fermi surface topology, total and partial densities of electronic states for BaTi2Bi2O obtained by means of the first-principles FLAPW-GGA calculations. The inter-atomic bonding picture is described as a high-anisotropic mixture of metallic, covalent, and ionic contributions. Besides, the structural and electronic factors, which can be responsible for the increased transition temperature for BaTi2Bi2O (as compared with related pnictide-oxides BaTi2As2O and BaTi2Sb2O), are discussed.

Structural, electronic properties, and chemical bonding in quaternary layered titanium pnictide-oxides Na2Ti2Pn2O and BaTi2Pn2O (Pn = As, Sb) from FLAPW–GGA calculations

By means of the first-principles FLAPW–GGA calculations, we have investigated the main trends in structural, electronic properties, and chemical bonding for a series of quaternary titanium pnictide-oxides: Na2Ti2As2O, Na2Ti2Sb2O, BaTi2As2O, and BaTi2Sb2O, which attracted now much attention as parent phases for a novel group of layered Fe-free superconducting materials. Our results cover the optimized lattice parameters and atomic positions, electronic bands, Fermi surface topology, total and partial density of electronic states. Besides, Bader analysis and the charge density maps are used to discuss the chemical bonding for the examined materials. We find that the atomic substitutions lead to anisotropic deformation of the crystal structure; this effect is related to strong anisotropy of inter-atomic bonds, which are of a mixed (covalent-ionic-metallic) type – in blocks [Ti2Pn2O], whereas the bonding between blocks [Ti2Pn2O] and atomic sheets of Na, Ba ions is of an ionic type. The actual effective atomic charges differ from the formal ionic charges due to covalency in blocks [Ti2Pn2O]. The near-Fermi electronic bands, which are responsible for metallic-like behavior of these materials and will be involved in the formation of superconducting state, arise mainly from the Ti 3dxy, dx2−y2, and dz2 states of the blocks [Ti2Pn2O], which define also the anisotropic character of conduction happening mainly in these blocks. The differences in the topology of the multi-sheet Fermi surfaces of these materials are discussed.

First Principle Study of the Structural, Electronic and Magnetic Properties of MgO Nanolayers on Fe Substrate

We have investigated the structural, electronic, and magnetic properties of MgO nanolayers with two different nanolayer thicknesses (1.5 nm and 1.75 nm) on a Fe substrate. The calculated results in this paper were obtained using the density functional theory (DFT) within the generalized gradient approximation (GGA). The total energies as a function of volume are calculated and thereby the lattice parameters, bulk moduli of MgO nanolayers with two different thicknesses have been calculated. The effects of surface atoms and Fe substrate atoms on physical properties of these nanolayers have been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states of MgO shows that this compound is an insulator in the nonmagnetic phase. MgO nanolayers on Fe substrate are metal in the ferromagnetic phase. The magnetic properties of surface atoms and Fe substrate atoms have been investigated and compared with bulk. Furthermore, the effect of hydrostatic pressure on the total and local magnetic moment of these nanolayers has been investigated.

Electronic Structure of Pt and Au Compounds Measured by X-ray Emission and X-ray Absorption Spectroscopies

The electronic structure of the filled and unfilled states and the formation of the chemical bonding in PtO2, PtCl4, PtS2, and Au2S are studied by measured Pt and Au Lβ5 X-ray emission spectra (XES) and L3-edge X-ray absorption spectra (XAS). The study is based on the comparative analysis of the calculated local partial densities of electronic states (LPDOS) on the noble atom and on the neighboring ligands. It is revealed that theoretical description of experimental spectra requires going beyond MT-approximation and therefore the full-potential linearized augmented-plane-wave method realized in the code WIEN2k is applied. The effect of a static screened 2p core-hole potential of Pt and Au on the calculated Pt L3-edge XAS is examined with a supercell approach. The obtained agreement of theoretical spectra with the experimental ones validates the results of the LPDOS analysis and the made conclusions on electronic structure of the studied compounds.

Electron energy spectrum in silicon-based Pd-substituted clathrate crystals

The results of the theoretical investigation of the electronic structure of the silicon-based Pd-substituted clathrates are presented. The calculation has been performed by the linearized augmented plane wave method. The calculation has resulted in the band structure, total and partial densities of electron states, and X-ray emission spectra. The influence of the number of substitutions in the unit cell on the electron energy spectrum of clathrates has been analyzed.

Electronic structure of Ti4Fe2O as determined from ab initio calculations and X-ray spectroscopy studies

The TiLα, FeLα and OKα ultrasoft X-ray emission bands obtained in experiment reflect, respectively, the energy distribution of mainly the Ti3d, Fe3d and O2p electronic states in Ti4Fe2O compound, which is an efficient hydrogen absorber for energy cells. Full and partial densities of electronic states for all atoms constituting the indicated oxide were calculated by a modified method of associated plane waves (APW) using the WIEN2k software package. The APW calculation data for Ti4Fe2O compound as well as superposition of TiLα, FeLα and OKα ultrasoft X-ray emission bands on a single energy scale indicate that O2p states in the oxide are localized mainly near the bottom of the valence band, the major contribution near the ceiling of the valence band belonging to Fe3d and Ti3d states. According to the APW calculation, the major contribution to the bottom of Ti4Fe2O conduction band is made by Fe3d* and Ti3d* states. The APW data for Ti4Fe2O are supported by the cluster calculation performed for this compound using a FEFF82 software package.

Study of local atomic and electronic structure of titanium-containing forsterite based on analysis of X-ray absorption spectra

The local atomic structure of titanium-containing forsterite is investigated based on analysis of X-ray absorption near-edge structure (XANES) spectra. The Ti K-XANES spectra of the mineral under study are calculated for several possible structural models. Theoretical analysis of the X-ray absorption spectra is performed based on the full-potential finite-difference method. The local geometry of the titanium environment is determined by comparing the experimental Ti K-XANES spectrum with the theoretical spectra calculated for different structural models. The structural model where titanium atoms substitute for silicon ones is found to be most likely for titanium-containing forsterite. The calculated partial densities of electron states of titanium near the bottom of the conduction band of titanium-containing forsterite are analyzed.

Structural, elastic, vibrational and electronic properties of amorphous Al2O3 from ab initio calculations

First-principles molecular dynamics calculations of the structural, elastic, vibrational and electronic properties of amorphous Al2O3, in a system consisting of a supercell of 80 atoms, are reported. A detailed analysis of the interatomic correlations allows us to conclude that the short-range order is mainly composed of AlO4 tetrahedra, but, in contrast with previous results, also an important number of AlO6 octahedra and AlO5 units are present. The vibrational density of states presents two frequency bands, related to bond-bending and bond-stretching modes. It also shows other recognizable features present in similar amorphous oxides. We also present the calculation of elastic properties (bulk modulus and shear modulus). The calculated electronic structure of the material, including total and partial electronic density of states, charge distribution, electron localization function and the ionicity for each species, gives evidence of correlation between the ionicity and the coordination for each Al atom.

Electronic structure and spectral characteristics of Zn-substituted clathrate silicides

The results of complex theoretical studies of the electron structure of Zn-substituted Si-based clathrates are reported. The calculation is carried out by the linearized augmented plane wave method. As a result, the energy band structures, the total and partial densities of electron states, and the X-ray emission spectra are obtained. The effect of the number of substitutions and their sites in the unit cell on the electron-energy spectrum of clathrates is analyzed.

Structural and electronic properties of Eu- and Pd-doped ZnO

Doping ZnO with rare earth and 4d transition elements is a popular technique to manipulate the optical properties of ZnO systems. These systems may also possess intrinsic ferromagnetism due to their magnetic moment borne on 4f and 4d electrons. In this work, the structural, electronic, and magnetic properties of Eu- and Pd-doped ZnO were investigated by the ab initio density functional theory methods based on generalized gradient approximation. The relative stability of incorporation sites of the doped elements in the ZnO host lattice was studied. The ground state properties, equilibrium bond lengths, and band structures of both the ZnO:Eu and ZnO:Pd systems were also investigated. The total and partial densities of electron states were also determined for both systems. It was found that in the ZnO:Eu system, ambient ferromagnetism can be induced by introducing Zn interstitial which leads to a carrier-mediated ferromagnetism while the ZnO:Pd system possesses no ferromagnetism.PACS 31.15.E-, 75.50.Pp, 75.30Hx

Emergence of Superconductivity in LaOFeAs: Electronic Structure and Lattice Dynamics

In view of continuing interest in the parent compound of the recently discovered superconducting iron-oxypnictide (LaO1-xFxFeAs) we present fresh results and analyses of ab-initio calculations of the electronic band structure, lattice dynamical properties, and elastic constants assuming it to be insulating as well as metallic. The total and partial electronic density of states (EDOS) of the undoped LaOFeAs in both states are extracted from the electronic band structure. The phonon dispersion and the phonon density of states (PDOS) are also studied. Possible implications of the band structure, EDOS, and PDOS of LaOFeAs on the eventual appearance of high-Tc superconductivity upon carrier doping are discussed. Our findings reveal that phonons are unlikely to mediate Cooper pairing in RE-OFeAs. In addition, the values of various independent elastic constants of the compound assuming both insulating and metallic states are estimated and discussed. Keywords: LaOFeAs; Electronic band structure; Phonon spectrum; Elastic constants; Superconductor.© 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi:10.3329/jsr.v3i1.6211 J. Sci. Res. 3 (1), 1-11 (2011)

Structural, Electronic and Magnetic Properties of Nanolayer and Bulk of MnCo2Si and MnFeCoSi Compounds

In the present work we have investigated the structural, electronic and magnetic properties of MnCo2Si and MnFeCoSi in bulk and nanolayer using density functional theory. The total energies as a function of volume are calculated and thereby the bulk modulus and their pressure derivatives are determined. The effect of atoms at the surface of these nanolayers has been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states show that both bulk MnCo2Si and MnFeCoSi present a half-metallicity, which is lost at their nanolayer surfaces. Furthermore, the effects of pressure on the magnetic moment of these compounds in its bulk form are investigated.

Electron structure and spectral characteristics of Cd-substituted Ge-based clathrates

Theoretical data on the electron energy spectrum of the substituted clathrates in the Ba-Cd-Ge system with different content of Cd atoms are reported. The calculation is carried out by the method of linearized augmented plane wave. The energy band structures, the total and partial densities of electron states, and the X-ray emission spectra are obtained from the calculations.

Investigation of tetragonal ReN 2 and WN 2 with high shear moduli from first-principles calculations

Two new transition metal dinitrides, ReN 2 and WN 2, with the P 4 / mmm structure are investigated by the first-principles calculations. The computed shear moduli of 327 GPa for ReN 2 and 334 GPa for WN 2 exceed those of all transition metal dinitrides previously reported. The estimated theoretical hardness are 46.3 GPa for ReN 2 and 47.9 GPa for WN 2, respectively. The calculated high shear moduli and hardness indicate that they are potential ultrahard materials. It is important to note that the computed hardness of the weakest bond are 34.7 GPa (W–N) for WN 2 and 33.1 GPa (Re–N) for ReN 2, much higher than that of 21.1 GPa (Re–B) for ReB 2, which suggests that tetragonal ReN 2 and WN 2 are probably harder than ReB 2. The total and partial electron density of states and the electron localization function for ReN 2 and WN 2 are analyzed. We attribute the high bulk modulus, shear modulus, and hardness to a three-dimensional covalently bonded framework in tetragonal ReN 2 and WN 2. Our calculations show that tetragonal ReN 2 is expected to be synthesized above 62.7 GPa and tetragonal WN 2 may be hard to be synthesized.

The electronic structure of alkali metal oxides

Crystalline phase total energies, band structures, the distributions of the total and partial densities of electron states, and atomic charges were calculated for lithium, sodium, and potassium oxides, peroxides, superoxides, and ozonides using the CRYSTAL 06 and GAMESS packages in the B3LYP parameterization. For the molecular phases, the geometry was optimized and molecular orbital energies calculated. The results obtained for metal oxides were compared with the experimental photoelectron spectroscopy data and used to analyze their formation and thermal decomposition.

Electronic structure of ilmenite: X-ray absorption and DFT study

The experimental Ti K-edge X-ray absorption near edge structure (XANES) spectrum of the mineral ilmenite was recorded. The theoretical Ti K-XANES spectra of ilmenite were simulated using both the self-consistent real-space full-multiple scattering theory within the muffin-tin approximation for the potential shape and the full-potential finite difference method. The comparison of the theoretical spectra with the experimental XANES is discussed. The electronic structure of ilmenite was investigated by analyzing the distribution of the partial densities of electron states.