Calculation of the density of states of NbNx by the recursion method

The density of states, n(E), of NbN_x has been calculated by means of the Recursion Method for x ? 1. The results have been compared with experiment, obtaining that the most important trends of the density of states are reproduced fairly well, even if the variation of the density of states at the Fermi level, as a function of the concentration of N-impurities cannot be predicted.     

Electronic structure and magnetic susceptibility of monoclinic α-plutonium

The electronic structure of the α-phase of plutonium has been calculated by the band methods with allowance for the spin-orbit interaction and Coulomb correlations in the complete matrix form (the LDA + U + SO method). The strong spin-orbit interaction of the 5 f electrons is manifested in the splitting of the calculated density of the 5f states, which makes a small contribution at the Fermi level on the order of the contribution from the 6d states. Using the results of the ab initio calculations, the spin and orbit contributions to the magnetic susceptibility of α-plutonium have been determined. Along with the impurity contribution, they describe well the experimental data on the susceptibility of this plutonium phase to a temperature of 300 K.     

Ab initio study of structural, electronic and optical properties of Be-doped CdS, CdSe and CdTe compounds

Full-potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method within density functional theory (DFT) has been utilized to calculate structural, electronic and optical properties of Be-doped CdS, CdSe and CdTe compounds with the dopant concentration x in the range 0≤x≤1. For the contribution of exchange-correlation potential, we used Wu-Cohen generalized gradient approximation (GGA) to calculate structural parameters, whereas both Wu-Cohen and Engel-Vosko GGA have been applied to calculate electronic structure of the materials. Only a slight deviation from Vegard's law has been observed for the calculated lattice constants and bulk moduli of the alloys. Structural and chemical factors that affect the band-gap bowing of these semiconductor alloys have been estimated and discussed. Density of states curves and charge density maps have been calculated and analyzed. Lastly, optical properties of both binary and their related ternary alloys have been discussed in terms of the calculated dielectric function. The resultant optical parameters are compared with the available experimental data and other calculations.     

Valence band density of states of amorphous and trigonal selenium determined by X-ray and U.V. photoemission

The densities of states of the entire valence bands of amoprhous and trigonal selenium have been measured by X-ray (hv = 1486.6 eV) and u.v. (hv = 21.2 eV) photoemission. It is found that the primary differences in the density of states of the two forms occurs in the p-like valence bands, in particular the lower bonding set. The density of states calculated by Kramer et al. for the amorphous form is shown to be in better agreement with the experimental density of states of the trigonal form than with that of the amorphous form.     

The ferromagnetic to paramagnetic phase transition of Fe studied by x-ray photoelectron spectroscopy

Valence band x-ray photoelectron spectra from Fe(100) have been measured as a function of temperature to above the Curie temperature, T_c. The room temperature data can be reconciled with the theoretical one-particle density of states (DOS). At T = 1.034T_c, the data do not resemble the paramgnetic DOS of Fe as calculated in the disordered-local-moment limit.     

A comparative study of the density of defect states in bulk samples and thin films of glassy Se<Subscript>90</Subscript>Sb<Subscript>10</Subscript>

The present paper reports the comparative study of density of defect states (DOS) between bulk samples and thin films of glassy Se₉₀Sb₁₀. These glasses have been prepared by the quenching technique. Thin films of these glasses have been prepared by vacuum evaporation technique. Space-charge-limited conduction (SCLC) has been measured at different temperatures. The density of localized states near Fermi level is calculated by fitting the data to the theory of SCLC for the case of uniform distribution of localized states for bulk as well as for thin films. A comparison has been made between the density of states calculated in these two cases.     

Vacancy defects in delafossite СuАlO<Subscript>2</Subscript>: First-principles calculations

Electronic properties and formation energies of vacancy defects in delafossite CuAlO₂ have been investigated by using the first-principles density functional theory. The band structures and density of states of various vacancy defects have been obtained and analyzed. The results show that the V _Cu systems with different charge states influence the type of conductivity. The introduced vacancy defects enhance the hybridization between O-2p and Cu-3d states, which is good for p-type conductivity. The calculated formation energies indicate that the Cu vacancy is relatively easy to form and it trends to have positive charge.     

Measurements and calculations of photoemission from Ca

The band structure, density of states and photoemission energy distributions for calcium have been calculated from a muffin-tin potential. Photoemission energy distributions have been measured. Transitions between s-p bands are identified. Structure from the empty d-states does not contribute to the primary distribution but is observed in the scattered one.     

Optical and photoemission properties of alkali-metal nitrates

The reflection and photoemission spectra of sodium, potassium, rubidium, and cesium nitrates were recorded in the energy interval 5–11.5 eV. The band structure, density of electronic states, and optical functions are calculated within the context of the density functional theory by the pseudopotential method in the basis set of localized sp ³ d ⁵ atomic pseudoorbitals expanded in the plane waves. The experimental and theoretical data are compared, and it is shown that the calculated spectral dependences of the imaginary part of the complex dielectric constant and combined density of states are in satisfactory agreement with the observed reflection and photoemission spectra, which suggests that the processes governed by these phenomena have the zone nature.     

Effect of copper and cobalt impurities on the electronic structure and optical spectra of the intermetallic compound PrNi5

The electronic structure and optical properties of the intermetallic compound PrNi₅ and their evolution during the substitution of copper or cobalt atoms for nickel atoms have been investigated. The band spectra of the studied compounds have been calculated in the local spin density approximation corrected to account for strong electron-electron interactions in the 4f shell of the rare-earth ion (LSDA + U method). The dispersion relations of the optical conductivity in the interband light absorption region have been interpreted using the results of calculations of the electron density of states.     

Electron impact excitation of highly charged sodium-like ions

Oscillator strengths, transition probabilities and collision strengths for transitions between n = 3 and n = 4 levels in Ca(X), Fe(XVI), Zn(XX), Kr(XXVI) and Mo(XXXII) have been calculated in a non-relativistic approximation. Wave functions of excited states have been obtained using a semi-empirical procedure. Collision strengths for electron-impact excitation have been calculated in a distorted wave approximation without exchange.Relative intensities of certain emission lines in the sodium isoelectronic sequence are density dependent. An example of this dependence is discussed in the text.     

Lattice dynamics properties of XAs (X=Al,Ga and In) with zinc-blende structure from first-principle calculations

Band structures, density of states, dielectric and vibrational properties of XAs (X=Al, Ga and In) alloys with zinc-blende structure have been studied using the density functional theory (DFT). The calculated lattice constants, band gap, static dielectric constants and phonon frequencies are all in good agreement with the available experimental data and other theoretical results. The calculated results show that Born effective charges Z_B increase with cation mass. A similar tendency has been observed for phonon frequencies ω_TO and ω_LO. Calculation results prove that static dielectric constants ε(0) increase with atomic weight, i.e. in the sequences AlAs–GaAs–InAs, and show an inverse sequence for band gap.     

Hydrogen storage: Lattice dynamics of orthorhombic NaMgH3

In this work, we investigate the structural, dynamic and thermodynamic properties of NaMgH₃, devoted for hydrogen storage. Density functional theory using pseudopotential methods and generalized gradient approximation has been used. A good agreement between the calculated structural parameters and the experimental data was found. A linear-response approach for the density functional theory is used in order to derive the Born effective charge tensors, the dielectric permittivity tensors, the phonon frequencies at the center of the Brillouin zone, the phonon-dispersion curves and the corresponding density of states for NaMgH₃ material. The obtained phonon frequencies at the zone center (Γ point) for the Raman-active and infrared-active modes are analyzed. Thermodynamic functions using the phonon density of states are also calculated.     

Effect of the local coulomb interaction of strongly correlated electrons on phonon, elastic, and electronic properties of ZnSe crystals

The dispersions and densities of states of phonons in cubic ZnSe crystals have been calculated and the modification of these quantities with inclusion of the local Coulomb interaction U of strongly correlated 3d(Zn) electrons has been investigated. It has been found that the inclusion of U leads to a decrease in the frequencies of optical and longitudinal acoustic phonons and to an increase in the frequencies of transverse acoustic phonons in the entire Brillouin zone. To explain these specific features in the behavior of phonons, the modifications of elastic moduli and electron density of states with inclusion of U have been analyzed.     

Theoretical and experimental study of the electronic structure of tin dioxide

The electronic structure of tin dioxide has been theoretically studied within the linearized augmented plane wave method using the Wien2k program package. The total and local partial electron densities of states have been calculated. The X-ray emission K-spectrum of oxygen has been calculated. The X-ray absorption spectra of the tin M _4,5-edge and oxygen K-edge have been calculated by simulating the supercell and core hole. The calculated results have been compared with the experimental data obtained using synchrotron radiation.     

Adsorption on graphene with vacancy-type defects: A model approach

The influence of graphene lattice defects on the adsorption properties of graphene has been considered. The adsorption properties have been investigated in the framework of the Anderson model. The disorder of the graphene crystal lattice has been analyzed using the T-matrix approximation. It has been found that the characteristic energy levels of defects are located near the Dirac point (±1 eV), because the most significant distortions of the spectrum due to the presence of defects in the graphene crystal lattice are observed in the vicinity of this point. Analytical expressions for the density of states of disordered graphene and atoms adsorbed on it have been obtained. A numerical calculation of the charge transfer in the considered system has been carried out. The obtained values of the charge transfer are in good agreement with the results of other studies, where the charge transfer was calculated using the experimental data and the density functional theory method. In the absence of defects, the presented results are well consistent with the results obtained within the M-model of adsorption (Davydov model). An approximation for the density of states of disordered graphene and the shift function of an adsorbed atom has been proposed. This approximation allows one to obtain analytical expressions for the charge transfer, energy of adsorption, and dipole moment.     

The effect of transition probability on the shape of X-ray photoelectron spectra of diamond and silicon

X-ray photoelectron spectra of valence bands in diamond and silicon have been calculated. It is shown that the probability of electron excitation from s-states is higher than that from p-states. The density of the electron states in the valence band of these crystals differs markedly from the energy distribution of photoelectrons.     

Structural,electronic, optical and bonding properties of strontianite,SrCO3: First-principles calculations

The first-principles calculations are performed within the density functional theory to investigate the crystal structure, energy band structure, density of states, optical properties, and bonding properties of strontianite. The optimized structure parameters and bonding results with the generalized gradient approximation (GGA) functional and the localized density approximation (LDA) functional are in good agreement with the earlier experimental data. The band structure, density of states and chemical bonding of strontianite have been calculated and analyzed. The indirect band gap of strontianite is estimated to be ~4.45 eV (GGA) or ~4.24 eV (LDA). The absorption, reflectivity, refractive index and extinction coefficient have been calculated using the imaginary part of the dielectric function. The calculated results of the optical properties show that strontianite has an optical anisotropy along [100] (or [010]) and [010] polarization directions of incoming light. Furthermore, the calculated results of the density of states and Mulliken population indicate that the interactions among atoms are both ionic and covalent bonding in strontianite.     

First principles study of structural, elastic, electronic and optical properties of the cubic perovskite BaHfO3

First principles study of structural, elastic, electronic and optical properties of the cubic perovskite-type BaHfO₃ has been reported using the pseudo-potential plane wave method within the local density approximation. The calculated equilibrium lattice is in a reasonable agreement with the available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. Band structures show that BaHfO₃ is a direct band gap between the occupied O 2p and unoccupied Hf d states. The variation of the gap versus pressure is well fitted to a quadratic function. Furthermore, in order to understand the optical properties of BaHfO₃, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. We have found that O 2p states and Hf 5d states play a major role in the optical transitions as initial and final states, respectively. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of BaHfO₃ compound, and it still awaits experimental confirmation.