A. L. Ivanovskii

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.

Electronic structure of superconducting MgB 2 and related binary and ternary borides

First-principles full potential linear muffin-tin orbital--generalized gradient approximation electronic structure calculations of the new medium-T{sub C} superconductor (MTSC) MgB{sub 2} and related diborides indicate that superconductivity in these compounds is related to the existence of p{sub x,y}-band holes at the {Gamma} point. Based on these calculations, we explain the absence of medium-T{sub C} superconductivity for BeB{sub 2}, AlB{sub 2}, ScB{sub 2}, and YB{sub 2}. The simulation of a number of MgB{sub 2}-based ternary systems using a supercell approach demonstrates that (i) the electron doping of MgB{sub 2} (i.e., MgB{sub 2-y}X{sub y} with X=Be, C, N, O) and the creation of defects in the boron sublattice (nonstoichiometric MgB{sub 2-y}) are not favorable for superconductivity, and (ii) a possible way of searching for similar or higher MTSC should be via hole doping of MgB{sub 2} (CaB{sub 2}) or isoelectronic substitution of Mg (i.e., Mg{sub 1-x}M{sub x}B{sub 2} with M=Be, Ca, Li, Na, Cu, Zn) or creating layered superstructures of the MgB{sub 2}/CaB{sub 2} type.

Band structure and properties of superconducting MgB2 and related compounds (A review)

This paper presents an overview of the current state of the art in research into the electronic structure and properties of a new superconductor, namely, MgB2, and a large number of related compounds by computational methods of the band theory. Consideration is given to the specific features of the surface states of magnesium diboride, the electron and hole doping effects in this compound, and the concentration dependences of the band structure and the properties of Mg1−xMexB2 and MgB2−yXy solid solutions and a number of superstructures. The electronic properties of AlB2-like phases, boron, higher borides, a series of ternary layered boron-containing phases, and compounds with structures of the antiperovskite type (MgCNi3 and others) are discussed in terms of their superconducting characteristics. The results obtained in modeling nanotubes and fullerene-like nanoparticles based on MgB2 and related borides are analyzed.

New ternary ThCr2Si2-type iron–selenide superconducting materials: Synthesis, properties and simulations

Jiangang Guo,1 Shifeng Jin,1 Gang Wang,1 Shunchong Wang,1 Kaixing Zhu,1 Tingting Zhou,1 Meng He,2 and Xiaolong Chen1 1Research & Development Center for Functional Crystals, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, China 2National Centre for Nanoscience and Technology, Beijing 100190, China Received 4 October 2010; revised manuscript received 11 November 2010; published 29 November 2010

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 properties of single-walled V2O5 nanotubes

Abstract Atomistic models of quasi-one-dimensional vanadium pentoxide nanostructures—single-walled nanotubes formed by rolling (010) layers of V 2 O 5 are constructed and their electronic properties and bond indices are studied using the tight-binding band method. We show that all zigzag ( n ,0)- and armchair ( n , n )-like nanotubes are uniformly semiconducting, and the band gap trends to vanish as the tube diameters decrease. The V–O covalent bonds were found to be the strongest interactions in V 2 O 5 tubes, whereas V–V bonds proved to be much weaker.

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.