Trends in structural and electronic properties for layered SrRu2As2, BaRu2As2, SrRh2As2 and BaRh2As2 from ab initio calculations

Based on first-principle FLAPW-GGA calculations, we have investigated the systematic trends in structural and electronic properties of a newly discovered group of ThCr2Si2-like arsenides: SrRu2As2, BaRu2As2, SrRh2As2 and BaRh2As2. Our results show that the replacement of an alkaline earth metal (Sr - Ba) and 4d metal (Ru - Rh) leads to various types of anisotropic deformations of the crystal structure caused by strong anisotropy of inter-atomic bonds. The band structure, density of states and Fermi surfaces have been evaluated and discussed. Appreciable changes in the near-Fermi bands and the Fermi surface topology found as going from (Sr,Ba)Ru2As2 to (Sr,Ba)Rh2As2 reflect the growth of the 3D-like type of dispersion for these systems, which is accompanied by an increase in the near-Fermi density of states. The inter-atomic bonding in (Sr,Ba)(Ru,Rh)2As2 phases adopts a complex anisotropic character, where the bonding in [(Ru,Rh)2As2] blocks is of a mixed metallic-ionic-covalent type whereas between adjacent [(Ru,Rh)2As2] blocks and (Sr,Ba) atomic sheets, ionic interactions emerge; thus these systems may be classified as ionic metals.Comment: 17 pages, 5 figure

Elastic properties and chemical bonding in ternary arsenide SrFe2As2 and quaternary oxyarsenide LaFeAsO - basic phases for new 38-55K superconductors

We report the first-principle FLAPW-GGA calculations of the elastic properties of two related layered phases, namely, the ternary arsenide SrFe2As2 and the quaternary oxyarsenide LaFeAsO - basic phases for the newly discovered "122" and "1111" 38-55K superconductors. The independent elastic constants (Cij), bulk moduli, compressibility, and shear moduli are evaluated and discussed. The numerical estimates of the elastic parameters of the polycrystalline SrFe2As2 and LaFeAsO ceramics are performed for the first time. Additionally, the peculiarities of chemical bonding in these phases are discussed.Comment: 8 pages, 2 figure

The band structure of hexagonal diborides ZrB2, VB2, NbB2 and TaB2 in comparison with the superconducting MgB2

The band structure and the Fermi surface of hexagonal diborides ZrB2, VB2, NbB2, TaB2 have been studied by the self-consistent full-potential LMTO method and compared with those for the isostructural superconductor MgB2. 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.Comment: 7 pages, 4 figure

Elastic properties of superconducting LiFeAs from first principles

The first-principles FLAPW-GGA calculations of the elastic properties of recently discovered superconducting LiFeAs are reported. The independent elastic constants (Cij), bulk modulus, compressibility, and shear modulus are evaluated and discussed. Additionally, numerical estimates of the elastic parameters of the polycrystalline LiFeAs ceramics are performed for the first time.Comment: 7 pager

Electronic properties and Fermi surface for new Fe-free layered 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.Comment: 7 pages, 3 figure

Electronic properties of superconducting Sr4V2Fe2As2O6 versus Sr4Sc2Fe2As2O6

First principle FLAPW-GGA calculations have been performed with the purpose to understand the peculiarities of band structure and Fermi surface topology for recently discovered superconductor: Sr4V2Fe2As2O - in comparison with isostructural phase Sr4Sc2Fe2As2O6. Our main finding is that the replacement of Sc on vanadium leads to drastic transformation of electronic, magnetic and conductive properties of these materials: as against non-magnetic Sr4Sc2Fe2As2O6 which is formed from non-magnetic conducting [Fe2As2] and insulating [Sr4Sc2O6] blocks, Sr4V2Fe2As2O6 consists from non-magnetic conducting [Fe2As2] blocks and [Sr4V2O6] blocks which exhibit magnetic half-metallic properties.Comment: 12 pages, 5 figure

Trends in structural, electronic properties, Fermi surface topology, and inter-atomic bonding in the series of ternary layered dichalcogenides KNi2S2, KNi2Se2, and KNi2Te2 from first principles calculations

By means of the FLAPW-GGA approach, we have systematically studied the structural and electronic properties of tetragonal dichalcogenides KNi2Ch2 (Ch = S, Se, and Te). Our results show that replacements of chalcogens (S -> Se -> Te) lead to anisotropic deformations of the crystals structure, which are related to the strong anisotropic character of the inter-atomic bonds, where inside the [Ni2Ch2] blocks, mixed covalent-ionic-metallic bonds occur, whereas between the adjacent [Ni2Ch2] blocks and K atomic sheets, ionic bonds emerge. We found that in the sequence KNi2S2 -> KNi2Se2 -> KNi2Te2 (i) the overall band structure (where the near-Fermi valence bands are due mainly to the Ni states) is preserved, but the width of the common valence band and the widths of the separate subbands and the gaps decrease; (ii) the total DOSs at the Fermi level also decrease; and (iii) for the Fermi surfaces, the most appreciable changes are demonstrated by the hole-like sheets, when a necklace-like topology is formed for the 2D-like sheets and the volume of the closed pockets decreases. Some trends in structural and electronic parameters for ThCr2Si2-type layered dichalcogenides, KNi2Ch2, KFe2Ch2, KCo2Se2, are discussed.Comment: 10 pagers, 6 figure

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 first-principles calculations? we have probed the peculiarities of the elecrtonic band structure and Fermi surface for the recently discovered layered superconductor LaO0.5F0.5BiSi2 in comparison with the parent phase LaOBiO2. The electronic factors prpmoting 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.Comment: 8 pages, 4 figure

First-principles study of electronic band structure and elastic properties of superconducting nanolaminate Ti2InC

The full-potential linearized augmented plane wave method with the generalized gradient approximation for the exchange-correlation potential (FLAPW-GGA) is used to predict the electronic and elastic properties of the newly discovered superconducting nanolaminate Ti2InC. The band structure, density of states and Fermi surface features are discussed. The optimized lattice parameters, independent elastic constants, bulk and shear moduli, compressibility are evaluated and discussed. The elastic parameters of the polycrystalline Ti2InC ceramics are estimated numerically for the first time.Comment: 11 pages, 3 figure

Structural, electronic properties and Fermi surface of ThCr2Si2-type tetragonal KFe2S2, KFe2Se2, and KFe2Te2 phases as parent systems of new ternary iron-chalcogenide superconductors

First principles FLAPW-GGA method was used for the comparative study of the structural and electronic properties of three related tetragonal ThCr2Si2-type phases KFe2Ch2, where Ch are S, Se, and Te. The main trends in electronic bands, densities of states and Fermi surfaces for AFe2Ch2 are analyzed in relation to their structural parameters. We found that at the anion replacements (SSeTe) any critical changes in electronic structure of KFe2Ch2 phases are absent. On the other hand, our analysis of structural and electronic parameters for hypothetical KFe2Te2 allows to assume that this system may be proposed as perspective parent phase for search of new iron-chalcogenide superconducting materials.Comment: 7 pages, 4 figure