I. R. Shein

Elastic properties of mono- and polycrystalline hexagonal AlB2-like diborides of s, p and d metals from first-principles calculations

We have performed accurate ab initio total energy calculations using the full-potential linearized augmented plane-wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange–correlation potential to systematically investigate elastic properties of 18 stable, metastable and hypothetical hexagonal (AlB2-like) metal diborides MB2, where M = Na, Be, Mg, Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ag and Au. For monocrystalline MB2, the optimized lattice parameters, independent elastic constants (Cij), bulk moduli (B) and shear moduli (G) are obtained and analyzed in comparison with the available theoretical and experimental data. For the first time, numerical estimates of a set of elastic parameters of the polycrystalline MB2 ceramics (in the framework of the Voigt–Reuss–Hill approximation), namely bulk and shear moduli, compressibility (β), Youngs modulus (Y), Poissons ratio (ν) and Lame coefficients (μ, λ), are performed.

Band structure of ZrB2, VB2, NbB2, and TaB2 hexagonal diborides: Comparison with superconducting MgB2

The band structure and Fermi surface parameters of ZrB2, VB2, NbB2, and TaB2 hexagonal diborides are considered in the framework of the self-consistent full-potential LMTO method in comparison with the relevant parameters of a MgB2 isostructural superconductor. The factors responsible for the superconducting properties of AlB2-like diborides are analyzed, and the results obtained are compared with previous calculations and available experimental data.

Band structure and the magnetic and elastic properties of SrFeO3 and LaFeO3 perovskites

The band structure and the magnetic and elastic characteristics of SrFeO3 and LaFeO3 perovskites with ferromagnetic and antiferromagnetic collinear spin configurations (of the A, C, and G types) are investigated using the ab initio pseudopotential method (the VASP program package) with the inclusion of the single-site Coulomb correlations (the LSDA + U formalism). It is shown that, in the pressure range 0–50 GPa, the most stable states are the ferromagnetic metal state for the SrFeO3 compound and the antiferromagnetic insulator state of the G type for the LaFeO3 compound.

Electronic structure and Fermi surface of new K intercalated iron selenide superconductor KxFe2Se2

Abstract Using the ab initio FLAPW-GGA method we examine the electronic band structure, densities of states, and the Fermi surface topology for a very recently synthesized ThCr 2 Si 2 -type potassium intercalated iron selenide superconductor K x Fe 2 Se 2 . We found that the electronic state of the stoichiometric KFe 2 Se 2 is far from that of the isostructural iron pnictide superconductors. Thus the main factor responsible for experimentally observed superconductivity for this material is the deficiency of potassium, i.e. the hole doping effect. On the other hand, based on the results obtained, we conclude that the tuning of the electronic system of the new K x Fe 2 Se 2 superconductor in the presence of K vacancies is achieved by joint effect owing to structural relaxations and hole doping, where the structural factor is responsible for the modification of the band topology, whereas the doping level determines their filling.

Structural, electronic and magnetic properties of η carbides (Fe3W3C, Fe6W6C, Co3W3C and Co6W6C) from first principles calculations

First-principles FLAPW-GGA calculations have been performed with the purpose to determine the peculiarities of the structural, electronic, magnetic properties and stability for a family of related η carbides M3W3C and M6W6C (where M=Fe and Co). The geometries of all phases were optimized and their structural parameters, theoretical density, cohesive and formation energies, total and partial densities of states, atomic magnetic moments have been obtained and analyzed in comparison with available theoretical and experimental data.

Electronic structure of new oxygen-free 38-K superconductor Ba1−xKxFe2As2 in comparison with BaFe2As2 from the first principles

Based on first-principle FLAPW-GGA calculations, we have investigated the electronic structure of the newly discovered oxygen-free 38-K superconductor Ba1−xKxFe2As2 in comparison with a parent phase—the tetragonal ternary iron arsenide BaFe2As2. The density of states, magnetic properties, near-Fermi band compositions, together with the Sommerfeld coefficients γ and the molar Pauli paramagnetic susceptibility χ have been evaluated. The results obtained allow us to classify these systems as quasi-two-dimensional ionic metals, where the conduction is strongly anisotropic, occurring only in the (Fe-As) layers. According to our calculations, in the case of the hole doping of BaFe2As2, the density of states at the Fermi level grows, which may be a factor promoting the occurrence of superconductivity for Ba1−xKxFe2As2. On the other hand, Ba1−xKxFe2As2 lies at the border of the magnetic instability and the pairing interactions might involve the magnetic or orbital fluctuations.

Elastic parameters of single-crystal and polycrystalline wurtzite-like oxides BeO and ZnO: Ab initio calculations

The structural and elastic parameters (elastic constants; bulk, shear, and Young’s moduli; Poisson’s ratios; and Lamé coefficients) for ideal wurtzite-like beryllium and zinc monoxides are calculated by the full-potential linearized augmented-plane-wave (FLAPW) method with the WIEN2k code. These parameters are approximated to those for polycrystalline oxides BeO and ZnO in the framework of the Voigt-Reuss-Hill model. The results of calculations are compared with the available experimental data and used to estimate numerically the velocities of sound and the Debye temperatures for BeO and ZnO polycrystals.

Elastic properties of superconducting MAX phases from first‐principles calculations

Using first-principles density functional calculations, a systematic study of the elastic properties for all known superconducting MAX phases (Nb 2 SC, Nb 2 SnC, Nb 2 AsC, Nb 2 InC, Mo 2 GaC, and Ti 2 InC) was performed. As a result, the optimized lattice parameters, independent elastic constants, indicators of elastic anisotropy, and brittle/ductile behavior as well as the so-called machinability indexes were calculated. We also derived bulk and shear moduli, Youngs moduli, and Poissons ratios for ideal polycrystalline MAX aggregates. The results obtained are discussed in comparison with available theoretical and experimental data and elastic parameters for other layered superconductors.

Electronic structure and properties of beryllium oxide

This review focuses on computer simulation studies of the nature of chemical bonding in BeO and its electronic structure and physicochemical properties. The capabilities of modern quantum-chemical methods are analyzed with application to various structural defects in BeO, phase equilibria in the Be-O system, pressure-induced polymorphic transformations of BeO, and its mechanical, thermal, and spectroscopic properties.

Electronic band structure and Fermi surface for new layered superconductor LaO0.5F0.5BiS2 in comparison with parent phase LaOBiS2 from first principles

By means of ab initio calculations, we have probed the peculiarities of the electronic band structure and Fermi surface for the recently discovered layered superconductor LaO0.5F0.5BiS2 in comparison with the parent phase LaOBiS2. The electronic factors promoting the transition of LaOBiS2 upon fluorine doping to superconducting state: inter-layer charge transfer, the evolution of the Fermi surface, and the dependence of the near-Fermi densities of states on x for LaO1 − xFxBiS2 are evaluated and discussed in comparison with the available experiments.