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Prepared by the precursor method, lithium-doped cadmium oxide samples were synthesized using mixed formates of Cd 1- x Li x (HCOO) 2 ·2H 2 O (0 ≤ x ≤ 0.075) as a precursor. NMR spectra were obtained on the lithium nuclei incorporated in cadmium oxide; and it is demonstrated that there is only one type of impurity centers to be found. The first-principle method using a projector augmented wave (PAW) approach is applied to carry out electronic band structure calculations and to analyze optical absorption spectra for the cases of lithium atoms occupying interstitial sites and of lithium atoms substituting for cadmium or oxygen atoms. Calculations are carried out to determine energy-efficient preferences for sites of impurity centers, which indicate as the most probable the presence of lithium atoms at the interstitial sites, with vacancies observed in the cadmium sublattice. The presence of lithium atoms at the interstitial sites appears to be explaining the conductivity increase and the red-shift of the absorption edge observed in experiments.

Combined ab initio and experimental study of Mg-, Ca-, Sr-, Ba-doped bismuth titanate pyrochlores (BTO) has been carried out. It is revealed that the substitution of bismuth atoms by alkaline earth elements is a preferable process rather than the substitution of titanium atoms according to the structural and energy parameters from the first-principles calculations. The pyrochlore-type compounds Bi1.5Mg(Ca)xTi2O7-δ have been obtained at x = 0.25. Bismuth titanate pyrochlores doped with Mg and Ca are wide-band semiconductor materials with the maximum of light absorption at wavelengths

New Bi1.5Mg0.9-xLixNb1.5O7–δ (x = 0.25; 0.40) and Bi1.4RE0.1Mg0.5Li0.4Nb1.5O7–δ (RE – Eu, Ho, Yb) compounds with the pyrochlore structure were synthesized. The displacements of the A-site atoms (96g) and O' ones (32e) as well as the Li and RE atoms distribution in the A-sites were determined. The dopant distribution was proven by ab initio calculations. The most preferable (Bi1.5Li0.5)(Nb1.5Mg0.5)O7 model was predicted with a direct band gap of 3.18 eV corresponding to the experimental Eg for Bi1.5Mg0.5Li0.4Nb1.5O7–δ. The thermal stability of the compounds in air up to 1100–1220 °C and the reducing atmosphere up to 400 °C was determined. The charge disbalance in the A2O' sublattice and the oxygen vacancies predetermine the dielectric behavior of the ceramics up to 200 °C, the mixed conductivity at high temperatures (T > 200 °C), and the proton transport up to 400 °C. © 2021 Elsevier Ltd. This work is supported by the German-Russian Interdisciplinary Science Center (G-RISC) funded by the German Federal Foreign Office via the German Academic Exchange Service (DAAD) (the research project No M-2020a-4_d), and by RFBR according to the research project No 19-03-00642 A. The study was performed using the equipment of the Center for Shared Use of Scientific Equipment ?Khimiya? of the Institute of Chemistry FRC Komi Science Center, Ural Branch of the Russian Academy of Science. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III using beamline P02.1.

Iron and carbon doped nanostructured titanium dioxide with different morphology of aggregates was synthesized using the developed precursor technique. Glycolate of the general composition Ti1-xFex(OCH2CH2O)2-x/2 (0 ≤ x ≤ 0.1) was used as a precursor. The synthesized samples of the compositions Ti1-xFexO2, Ti1-xFexO(2-x/2)-yCy and Ti1-xFexO(2-x/2)-yCy:nC were characterized by X-ray diffraction, scanning electron microscopy, ultraviolet and visible absorption spectroscopy, as well as by vibration and X-ray photoelectron spectroscopy methods. In addition, they were tested as photocatalysts in the hydroquinone oxidation reaction under ultraviolet and visible irradiation. It is established that the insertion of iron into the structure of carbon-doped anatase (TiO2-yCy) suppresses its photocatalytic activity in the visible range of the spectrum, but leads to no change under ultraviolet irradiation. Globular samples of Ti1-xFexO(2-x/2)-yCy containing no more than 2.5 at% Fe show the maximum photocatalytic activity. To clarify the reasons for the observed complex dependence of photocatalytic activity on the concentration of the dopant first-principles, calculations of the electronic band structure and optical absorption of anatase doped with iron and carbon are performed and discussed.

For the first time the comparison of the theoretical and experimental data have shown that UV–vis absorption in the region of 600 nm in colloidal solution of NbS 3 can be described by the d-d electronic transitions to the antibonding molecular orbital. It is proved that the process leads to excitation of metal-metal bond.

The disordered perovskite-like phase LaCu0.5Ti0.5O3±δ (LCTO) with Pnma space group is synthesized by solid-state reaction route. Coulometric and thermogravimetric measurements in 300–1223 K temperature and 10−16 – 0.21 atm oxygen partial pressure ranges reveal narrow equilibrium oxygen content interval for the studied compound. Moreover, LCTO is shown to possess both over- and non-stoichiometry depending on external conditions. The complete reduction of LaCu0.5Ti0.5O3±δ results in a formation of La2O3, La2Ti2O7–x oxides and metallic copper. Defect chemistry modeling and DFT calculations evidence oxygen vacancies formed in LaCu0.5Ti0.5O3±δ at reduction can be considered mobile species. A decomposition mechanism for studied cuprate is proposed based on experimental results.

The ab initio projector augmented wave method of the density functional theory is applied for studying energy characteristics of oxygen vacancies and migration pathways in Pr1−xYxBaCo2O6−δ. It is found that the negative formation energy leads to initial appearance of oxygen vacancies in PrO planes thus providing the pathway for oxygen migration at small δ's. The increase of oxygen vacancy population in PrO planes and replacement of Pr by Y both favor a weakening of Co O bonds, which facilitates the increase in the amount of oxygen vacancies in CoO2 layers. Moreover, the yttrium dopants enlarge the bottleneck for oxygen jumps along ⟨101⟩ directions over oxygen vacancies in PrO and CoO2 layers. As a result, the respective ‘zigzag’ oxygen migration pathway becomes predominant with increasing oxygen non-stoichiometry and yttrium doping. Thus, the layered perovskite-like cobaltites give an example of a peculiar diffusion process where minority defects provide the transport channel while majority defects maintain favorable geometry of the migration pathway.

Based on the results of ab initio band structure calculations it was found that in a series of ternary and quarternary compounds (some antiperovskites, 1111-oxyarsenides and non-centrosymmetric superconductors) containing the atoms of platinum-group metals the latter reveal the anionic behavior. They are characterized with negative effective atomic charges, and the character of electronic density distribution in these crystals confirms the electronic transfer from cations towards platinum-groups metal atoms, as well as towards the atoms of non-metals. The possible reasons why platinum-groups metal atoms can rival with non-metallic atoms for being anions are briefly discussed.

Very recently, on the example of hole- and spin-doped BaZn2As2, quite an unexpected area of potential applications of 122-like phases was proposed as a promising platform for searching the new diluted magnetic semiconductors (DMSs) (2013; K. Zhao, et al, Nature Commun. 4:1442). Herein, by means of the first-principles calculations, we have examined in detail the basic structural, elastic, electronic properties and the peculiarities of the inter-atomic bonding in α and β polymorphs of 122-like BaZn2As2 – a parent phase of the new DMSs. Our characterization of these materials covers the optimized structural parameters, the main elastic parameters (elastic constants, bulk, shear, and Young’s moduli, Poisson’s ratio, anisotropy indexes, and Pugh’s criterion), as well as electronic bands and densities of electronic states.

The 6,7Li NMR spectra and the 7Li spin–lattice relaxation rate were measured on polycrystalline samples of Li2ZrO3, synthesized at 1050 K and 1300 K. The 7Li NMR lines were attributed to corresponding structural positions of lithium Li1 and Li2 by comparing the EFG components with those obtained in the first-principles calculations of the charge density in Li2ZrO3. For both samples the line width of the central 7Li transition and the spin–lattice relaxation time decrease abruptly at the temperature increasing above ~500 K, whereas the EFG parameters are averaged (〈νQ〉=42 (5) kHz) owing to thermally activated diffusion of lithium ions.

Very recently, low-temperature superconductivity was discovered for the intermetallic compound HfCuGe2 (2013; Cava RJ, et al, EPL 101:67001.), which was declared as "a non-magnetic analog of the 1111 iron pnictides". Herein, by means of the first-principles calculations, we have examined in detail the structural, elastic, and electronic properties of HfCuGe2, as well as of the isostructural and isoelectronic phases ZrCuGe2, HfCuSi2, and ZrCuSi2, which are analyzed in comparison with a set of 1111-like phases. The obtained close similarity of the electronic factors, namely, the topologies of the near-Fermi bands, the Fermi surfaces, as well as the DOS values at the Fermi level for superconducting HfCuGe2 and other examined 112 phases allowed us to assume that low-temperature superconductivity may be expected also for ZrCuGe2, HfCuSi2, and ZrCuSi2. © 2013 Elsevier Ltd. All rights reserved.

By means of the first principles calculations, the influence of arsenic deficiency on the electronic and magnetic properties of the layered phase LaFeAsO was examined. We found that As vacancies affect mainly the near-Fermi Fe-derived bands leading to their splitting and changing their dispersion and the level of filling. The Fermi surface for LaFeAs1−xO adopts a complicated multi-sheet morphology, with a number of linked 2D-like sheets and a set of new sheets (which are absent for ideal LaFeAsO) at the lateral sides of the Brillouin zone. Besides, for the most stable As-deficient phase an antiferromagnetic stripe-like spin configuration was found, for which an inhomogeneous distribution of magnetic moments of Fe atoms arises near and away from vacancy owing to differences in local magnetic moments of non-equivalent Fe atoms.

This work reports on the elastic, electronic properties and inter-atomic bonding of the newly discovered superconductor Th2NiC2 as obtained within ab initio calculations. We found that Th2NiC2 is mechanically stable and it will behave as a ductile material exhibiting enhanced elastic anisotropy in shear and a rather low hardness. The inter-atomic bonding in Th2NiC2 is described as an anisotropic mixture of covalent and ionic contributions, where inside [Th2C2] blocks covalent Th–C bonds emerge, and these blocks are bonded with the Ni atomic sheets through directional Ni–C bonds. Additionally, some inter-atomic ionic Th–C interactions occur owing to charge transfer Th → C. Our data reveal that for Th2NiC2 the Fermi level is located in a deep DOS minimum and the experimentally observed increase in TC in the sequence Th2NiC2 → Th1.8Sc0.2NiC2 may be explained by the growth of N(EF). We also speculate that an increase in N(EF) (and, probably, in TC) for Th2NiC2-based materials may be also achieved by an alternative way: by electron doping – for example, by partial substitution of V for Th or Cu for Ni, as well as by partial substitution of N for C with the formation of Th–Ni carbonitrides like Th2NiC2−xNx.

Very recently (2012, Phys. Rev Lett., 109, 035502) a new hexagonal (s.g. P63/mmc, ♯194) ternary phase Nb2GeC, which belongs to so-called 211-like MAX phases, was discovered. In order to get a systematic insight into the structural, elastic, and electronic properties of Nb2GeC, we used two complementary DFT-based first-principles approaches (as implemented in the VASP and Wien2k packages) to calculate the optimized structural parameters, band structure, densities of state, Fermi surface, and a set of elastic parameters: elastic constants (Cij), bulk modulus (B), compressibility (β), shear modulus (G), Young’s modulus (Y), and elastic anisotropy indexes, which were discussed in comparison with available data. Besides, the inter-atomic bonding picture for Nb2GeC was discussed using electron density maps and Bader’s charge analysis.

Employing first-principles band structure calculations, we have examined the electronic, optical properties and the peculiarities of the chemical bonding for six newly synthesized layered quaternary 1111-like chalcogenide fluorides SrAgSF, SrAgSeF, SrAgTeF, BaAgSF, BaAgSeF, and SrCuTeF, which are discussed in comparison with some isostructural 1111-like chalcogenide oxides. We found that all of the studied phases AMCh F ( A =Sr, Ba; M =Cu, Ag; and Ch =S, Se, Te) are semiconductors for which the fitted “experimental” gaps lie in the interval from 2.23 eV (for SrAgSeF) to 3.07 eV (for SrCuTeF). The near-Fermi states of AMCh F are formed exclusively by the valence orbitals of the atoms from the blocks ( MCh ); thus, these phases belong to the layered materials with “natural multiple quantum wells”. The bonding in these new AMCh F phases is described as a high-anisotropic mixture of ionic and covalent contributions, where ionic M–Ch bonds together with covalent M–Ch and Ch–Ch bonds take place inside blocks ( MCh ), while inside blocks ( A F) and between the adjacent blocks ( MCh )/( A F) mainly ionic bonds emerge.

Structural, electronic properties and relative stability of quasi-two-dimensional (2D) free-standing planar nano-block (NBs) structures Tin+1Al0.5Cn and Tin+1Cn (n = 1 and 2), which can be prepared using the recently developed procedure of exfoliation of corresponding NBs from MAX phases, were examined within first principles calculations in comparison with parent MAX phases Ti3AlC2 and Ti2AlC. We found that in general Tin+1Cn and Tin+1Al0.5Cn NBs retain the atomic geometries of the corresponding blocks of the MAX phases, but some structural distortions for the NBs occur owing to the lowering of the coordination number for atoms in the external Ti sheets of the nano-block structures. Our analysis based on their cohesive and formation energies reveals that the stability of the nano-block structures increases with index n (or, in other words, with a growth of the number of Ti–C bonds), the Al-containing NBs becoming more stable than the “pure” Ti–C NBs. Our data show that the magnetization of the simulated planar nano-block structures can be expected; so, for the Ti3C2 nano-block the most stable will be the spin configuration, where within each external Ti sheet the spins are coupled ferromagnetically together with antiferromagnetic ordering between opposite external titanium sheets of this nano-block.

The tetragonal (s.g. I 4/ nmm ; #129) silicide arsenide ZrCuSiAs is well known as a structural type of the broad family of so-called 1111-like quaternary phases which includes now more than 150 representatives. These materials demonstrate a rich variety of outstanding physical properties (from p-type transparent semiconductors to high-temperature Fe-based superconductors) and attracted a great interest as promising candidates for a broad range of applications. At the same time, the data about the electronic and elastic properties of the ZrCuSiAs phase itself, as well as of related silicide arsenides and germanide arsenides are still very limited. Here for a series of six isostructural and isoelectronic 1111-like phases which includes both synthesized (ZrCuSiAs, HfCuSiAs, ZrCuGeAs, and HfCuGeAs) and hypothetical (TiCuSiAs and TiCuGeAs) materials, systematical studies of their structural, elastic, electronic properties and stability trends are performed by means of first-principles calculations.

By means of first-principles calculations, we have systematically studied the structural, elastic, electronic, and thermodynamic properties of two related layered 122-type intermetallics: tetragonal LaNi 2 P 2 and LaNi 2 Ge 2 . The optimized lattice constants, cell volumes, electronic bands, Fermi surface topology, and densities of states were obtained and analyzed. We found that the bonding picture in the examined phases is of a complex anisotropic character and can be described as a mixture of metallic, ionic, and covalent contributions. We predicted that LaNi 2 P 2 , and LaNi 2 Ge 2 are mechanically stable and relatively soft materials with high compressibility and rather small hardness. Both phases will exhibit comparable elastic anisotropy and behave in a brittle manner. Sound velocities, Debye temperatures, and heat capacity C p ( T ) were evaluated for LaNi 2 P 2 and LaNi 2 Ge 2 in the low-temperature limit, and are in reasonable agreement with available experiments.

By means of the first principles FLAPW-GGA approach, a systematic study of the structural and electronic properties of full series of 15 synthesized and hypothetical tetragonal ThCr2Si2-type phases in the system A–Fe–Ch, where A = Li, Na, K, Rb, and Cs; Ch = S, Se, and Te, was performed. We find that for the tuning of the structural parameters of conducting [Fe2Ch2] blocks the replacements of Ch2− ions will be most effective, whereas for the tuning of the inter-blocks separation [Fe2Ch2]–[Fe2Ch2] the replacements of the alkaline ions seem more useful. The trends in the electronic properties and Fermi surface topology of AFe2Ch2 phases are analyzed in relation to their structural parameters to explore whether these materials can be as the parent systems for new ternary iron–chalcogenide superconductors. For all these systems, similar multi-sheet Fermi surfaces consist exclusively of electronic-like sheets, two of which are 2D-like sheets in the corners of the Brillouin zone, and the third one is a closed pocket around Z. The total DOSs at the Fermi level are related with the type of anion Ch2− and their values grow in the sequence AFe2S2 → AFe2Se2 → AFe2Te2. Thus we assume that AFe2Se2 and AFe2Te2 phases may be considered as favorable parent systems for the search of new ternary iron–chalcogenide SCs.

The structural, elastic, magnetic and electronic properties of the layered tetragonal phase KCo2Se2 have been examined in details by means of the first-principles calculations and analyzed in comparison with the isostructural KFe2Se2 as the parent phase for the newest group of ternary superconducting iron-chalcogenide materials. Our data show that KCo2Se2 should be characterized as a quasi-two-dimensional ferromagnetic metal with highly anisotropic inter-atomic bonding owing to mixed ionic, covalent, and metallic contributions inside [Co2Se2] blocks, and with ionic bonding between the adjacent [Co2Se2] blocks and K sheets. This material should behave in a brittle manner, adopt enhanced elastic anisotropy rather in compressibility than in shear, and should show very low hardness.

Using the first principles FLAPW-GGA method, comparative study of structural, electronic properties and of chemical bonding in four 1111-like chalcogenide oxides La MCh O (LaCuSO, LaCuSeO, LaAgSO, and LaAgSeO) with ZrCuSiAs-type structure was performed. Our studies showed that: (i) replacements of d metal atoms (Cu ↔ Ag) and chalcogen atoms (S ↔ Se) lead to anisotropic deformations of the crystal structure; this effect is related to strong anisotropy of inter-atomic bonds; (ii) all of the examined chalcogenide oxides are semiconducting; the band gap decreases both at S → Se and Cu → Ag substitutions; and (iii) the bonding in La MCh O phases can be classified as a high-anisotropic mixture of ionic and covalent contributions, where mixed covalent-ionic bonds take place inside [La 2 O 2 ] and [ M 2 Ch 2 ] blocks, whereas between the adjacent [La 2 O 2 ]/[ M 2 Ch 2 ] blocks, ionic bonds emerge owing to [La 2 O 2 ] → [ M 2 Ch 2 ] charge transfer. Since the near-Fermi bands of La MCh O phases originate mainly from electronic states of [ M 2 Ch 2 ] blocks, we speculate that chemical substitutions inside these blocks can result in striking differences in electronic properties of these systems; therefore, this approach can be promising for significant enlargement of the functional properties of these materials.

The tetragonal (s.g. I 4 / m m m ; #139) ThCr2Si2 is widely known as a structural type of the broad family of the so-called 122-like ternary phases which includes now more than 800 members. Among them the superconducting iron-pnictides A Fe 2 P n 2 (discovered in 2008, A = alkali -earth metals) and the newest superconducting iron-chalcogenides A ′ Fe 2 C h 2 (discovered in 2010, A ′ = alkali metals) have attracted recently enormous interest in this class of materials. Meanwhile, the data about the electronic, magnetic, and elastic properties of the ThCr2Si2 phase itself are still practically absent. Here, by means of first-principles calculations, the optimized structural parameters, spin ordering of the magnetic ground state, independent elastic constants, bulk, shear, and Young’s moduli, elastic anisotropy indexes, total and partial densities of states, and inter-atomic bonding picture for ThCr2Si2 were obtained for the first time and analyzed in comparison with the aforementioned most popular 122-like systems A Fe 2 P n 2 and A ′ Fe 2 C h 2 .

First-principles FLAPW-GGA band structure calculations were employed to examine the structural, electronic properties and the chemical bonding picture for four ZrCuSiAs-like Th-based quaternary pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO. These compounds were found to be semimetals and may be viewed as "intermediate" systems between two main isostructural groups of superconducting and semiconducting 1111 phases. The Th 5f states participate actively in the formation of valence bands and the Th 5f states for ThMPnO phases are itinerant and partially occupied. We found also that the bonding picture in ThMPnO phases can be classified as a high-anisotropic mixture of ionic and covalent contributions: inside [Th2O2] and [M2Pn2] blocks, mixed covalent-ionic bonds take place, whereas between the adjacent [Th2O2]/[M2Pn2] blocks, ionic bonds emerge owing to [Th2O2] \to [M2Pn2] charge transfer., 16 pages, 6 figures

Using the ab initio FLAPW-GGA method we have examined (Fe2As2)(Sr4 M 2 O6) phases (where M are Ti and Mg), to analyze the effect of replacements of d metals by sp elements in perovskite-type blocks as an effective way for the tuning of the electronic and structural properties of the recently synthesized 21113-type phases. We have found that unlike (Fe2As2)(Sr4Ti2O6), and (Fe2As2)(Sr4Mg2O6), where both building blocks are conducting, for (Fe2As2)(Sr4MgTiO6), conduction will happen exclusively in the [Fe2As2] blocks, whereas insulating [Sr4MgTiO6] blocks behave as “charge reservoirs” – as in other Fe-based superconductors. These data together with a set of so-called structural indicators (the a axis length, As Fe As bond angles, and anion height Δz) allow one to conclude that (Fe2As2)(Sr4MgTiO6) will be a promising superconducting material – in agreement with available experiments.

Using the ab initio FLAPW-GGA method, we have examined the structural, electronic, and magnetic properties of the newly synthesized layered tetragonal (space group P4/nmm) cobalt arsenide oxide (Co2As2)(Sr4Sc2O6) and the hypothetical (Co2P2)(Sr4Sc2O6) phase as Fe-free analogs of recently discovered isostructural superconducting materials (Fe2Pn2)(Sr4M2O6), where M are 3d metals such as Sc, Ti, and V, and Pn are pnictogens (P or As). For these Co-containing pnictide oxides, the optimized structural data, electronic bands, total and partial densities of states, Fermi surface topology, chemical bonding, and magnetic parameters have been obtained and analyzed in comparison with available experiments and with their Fe-based (Fe2As2)(Sr4Sc2O6) and (Fe2P2)(Sr4Sc2O6) analogs.

Based on first-principle FLAPW-GGA calculations, we have investigated structural and electronic properties of the recently synthesized tetragonal (space group P4/nmm) nickel-based pnictide oxide superconductors: 3.3 K (Ni 2 P 2 )(Sr 4 Sc 2 O 6 ) and 2.7 K (Ni 2 As 2 )(Sr 4 Sc 2 O 6 ). Optimized structural data, electronic bands, total and partial densities of states, and Fermi surface topology have been obtained and discussed in comparison with available experiments and with their Fe-based (Fe 2 P 2 )(Sr 4 Sc 2 O 6 ) and (Fe 2 As 2 )(Sr 4 Sc 2 O 6 ) analogs.

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 ThCr2Si2-type potassium intercalated iron selenide superconductor KxFe2Se2. We found that the electronic state of the stoichiometric KFe2Se2 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 KxFe2Se2 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., 10 pages, 3 figures

The atomic models of nanotubes for layered FeSe, LiFeAs, SrFe2As2, and LnFeAsO – the parent phases of so-called 11, 111, 122, and 1111 groups of newly discovered family of iron-based high temperature superconductors are proposed. On example of SrFe2As2 the electronic properties of predicted nanotubes are examined and discussed in comparison with those for the corresponding single layer and the crystal.

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 12 synthesized and hypothetical cubic antiperovskite-type Ni-rich nitrides MNNi 3 , where M are Zn, Cd, Mg, Al, Ga, In, Sn, Sb, Pd, Cu, Ag and Pt. As a result, the optimized lattice parameters, independent elastic constants ( C ij ), bulk-, shear- and tetragonal shear moduli, Cauchy’s pressure and some indexes of elastic anisotropy, as well as the numerical estimations of Young’s modulus, Poisson’s ratio and Pugh's indicator of brittle/ductile behavior for the corresponding polycrystalline MNNi 3 (in the Voigt-Reuss-Hill approximation) were obtained and analyzed in comparison with the available theoretical and experimental data.

The first-principle band structure calculations are employed to examine the influence of carbon non-stoichiometry on the structural and electronic properties of the cubic thorium monocarbide ThC. As a result, the equilibrium geometries, electronic bands, densities of states (DOS), Sommerfeld constants and Pauli paramagnetic susceptibility for ThC1−x (where x = 0, 0.25 and 0.50) are obtained and analyzed in comparison with available experimental data. Additionally, the formation energies of carbon vacancies are theoretically estimated for ThC1−x. The results obtained indicate that the introduction of carbon vacancies in ThC is accompanied by pronounced DOS changes due to the appearance of novel “vacancy states” in the near-Fermi region formed by comparable contributions of Th 6d and 5f states. The carbon deficiency strongly affects the structure and stability of thorium carbide. For example, for the hypothetical “over-deficient" composition ThC0.50 the initial cubic structure undergoes significant tetragonal distortions. On the contrary, for ThC0.75 the value of Evf is positive and the cubic structure of this phase is preserved.

Structural, elastic and electronic properties of the new ternary nitrides AlNNi3, GaNNi3 and InNNi3 with cubic antiperovskite-like structure have been predicted using the full-potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange–correlation potential.

Very recently the new low-temperature (TC∼3 K) superconductor (SC) SrPd2Ge2 has been reported. This compound is isostructural with curently intensively studied group of so-called “122” SCs (based on tetragonal AM2Pn2 phases, where A are Sr, Ba; M are d metals and Pn are pnictogens: As or P), but it is pnictogen-free. Here, by means of first-principle FLAPW-GGA calculations, we have studied the electronic structure of new SC SrPd2Ge2. The band structure, total and partial densities of states and Fermi surface topology for SrPd2Ge2 are evaluated and discussed in comparison with those of isostructural SrNi2Ge2 and SrNi2As2 phases.

We study structural, elastic, and electronic properties for three RuB 2 phases using ab initio total-energy calculations within the density functional theory. The orthorhombic and hexagonal structures are mechanically stable. More precisely, the orthorhombic is more stable than the hexagonal form. Results of bulk modulus, which are in good agreement with experimental data, show that the considered structures are potentially highly compressible materials. This is confirmed by the calculation of the hardness, indicating that RuB 2 is an ultracompressible material, but not a superhard material.

First principles FLAPW-GGA calculations have been performed to understand the peculiarities of stability, elastic, electronic properties and chemical bonding for cubic carbides of four noble metals M=Rh, Pd, Ir and Pt depending on carbon stoichiometry: MC versus M 4 C. Our main findings are as follows: (i) in contrast to mono -carbides MC with positive formation energies E form >0, carbon-deficient sub-carbides M 4 C are stable ( E form d –5 d metals (including P d and Pt examined here), an unusual effect of Rh and Ir “metallization” and the increasing of ductility for these metals owing to the introduction of carbon has been established.

We have performed ab initio total energy calculations using the full-potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient approximation (GGA) for the exchange-correlation potential to predict the structural, elastic, cohesive, electronic and magnetic properties of perovskite-like phases Co3WC, Rh3WC and Ir3WC. The optimized lattice parameters, density, independent elastic constants (Cij), bulk moduli, shear moduli, tetragonal shear moduli, compressibility, and Cauchy pressure, as well as electronic densities of states, cohesive and formation energies, atomic magnetic moments have been obtained and analyzed for the first time.

Very recently, the tetragonal BiOCuS was declared as a new superconducting system with a Fe-oxypnictide-related structure. Here, based on first-principle FLAPW-GGA calculations, the structural parameters, electronic band structure, density of states and inter-atomic bonding picture for BiOCuS are investigated. Our results show that, distinct from related metallic-like FeAs systems, the BiOCuS phase behaves as an ionic semiconductor with the calculated indirect band gap at about 0.48 eV. The superconductivity for BiOCuS may be achieved only by doping of this phase. Our data demonstrate that as a result of hole doping, the [CuS] blocks become conducting owing to mixed Cu 3d + S 3p bands located near the Fermi level. For the hole doped BiOCuS the Fermi surface adopts a quasi-two-dimensional-like character, similarly to FeAs SCs.

Very recently, the new 6 K superconductor (SC) LiFeP, the first arsenic-free analog of the family of the so-called “111” FeAs SCs, was discovered. Here, based on first-principle FLAPW-GGA calculations, the band structure, density of states, Fermi surface topology, electron density distribution and effective atomic charges for the new SC LiFeP are investigated for the first time and discussed in comparison with isostructural and isoelectronic LiFeAs. In addition, the theoretical shapes of FeL X-ray emission spectra for LiFeP and LiFeAs are evaluated and compared with available experiments.

We present FLAPW-GGA calculations of the magnetic and electronic properties of cubic RuN x ( x =1.0, 0.75 and 0.50). We find that RuN exhibits a ferromagnetic ground state and the local ruthenium magnetic moment abruptly decreases with nitrogen vacancies. The relative positions of t 2g and e g states and the Ru 4d–N 2p hybridization in RuN x are discussed. We have also found that the magnetic behavior for RuN x vs. FeN x as dependent on the nitrogen vacancies content displays an opposite trend.

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.

The comparative study of the structural, elastic, cohesive and electronic properties of three polymorphs (α-monoclinic, β-tetragonal and γ-cubic) of thorium dicarbide ThC2 is performed within the density-functional theory. The optimized atomic coordinates, lattice parameters, theoretical density (ρ), bulk moduli (B), compressibility (β), as well as electronic densities of states, electronic heat capacity (γ) and molar Pauli paramagnetic susceptibility (χ) for all ThC2 polymorphs are obtained and analyzed in comparison with available experimental data. The peculiarities of inter-atomic bonding for thorium dicarbide are discussed. Besides, we have evaluated the formation energies (Ef) of ThC2 polymorphs for different possible preparation routes (namely for the reactions with the participation of simple substances (metallic Th and graphite) or thorium monocarbide ThC and graphite). The results show that the synthesis of the ThC2 polymorphs from simple substances is more favorable – in comparison with the reactions with participation of Th monocarbide.

First principles calculations have been performed with the purpose to understand the comparative peculiarities of the structural, electronic properties and stability for all phases formed in the tungsten–carbon system: hexagonal and cubic mono -carbides WC and four polymorphs ( α , β , γ and e ) of semi -carbide W 2 C. All calculations were performed by means of the full-potential linearized augmented plane wave method (FLAPW). The generalized gradient approximation (GGA) in the Perdew–Burke–Ernzerhof (PBE) formalism was used for the exchange and correlation energy functional. The geometries of all WC and W 2 C phases were optimized and their structural parameters and theoretical density were established. Besides, we have evaluated the formation energies ( E form ) of all the tungsten carbides. Based on our estimations we can arrange all investigated W–C phases depending on their stability in the following sequence: h- WC> e -W 2 C> β -W 2 C> γ -W 2 C> α -W 2 C> c- WC. Here three carbides ( h- WC, e -W 2 C and β -W 2 C) are stable ( E form γ -W 2 C belongs to metastable systems ( E form ∼0), whereas α -W 2 C and c- WC appear to be unstable ( E form >0). Moreover, band structures, total and partial densities of states were obtained and analyzed systematically for all W–C phases in comparison with other available theoretical and experimental data.

Here we report the first-principle FLAPW-GGA calculations of the elastic properties of two related layered phases, namely, the ternary arsenide SrFe 2 As 2 and the quaternary oxyarsenide LaFeAsO – basic phases for the newly discovered “1 2 2” and “1 1 1 1” 38–55 K superconductors. The independent elastic constants ( C ij ), bulk moduli, compressibility, and shear moduli are evaluated and discussed. The numerical estimates of the elastic parameters of the polycrystalline SrFe 2 As 2 and LaFeAsO ceramics are performed for the first time. Additionally, the peculiarities of chemical bonding in these phases are discussed.

The full-potential linearized augmented plane wave method with a generalized gradient approximation for the exchange-correlation potential has been applied to predict the elastic properties of quaternary oxypnictides LaOFe Pn ( Pn = As and P) as the basic phases for the newly discovered 26–52 K superconductors. The optimized lattice parameters, independent elastic constants ( C ij ), bulk moduli, compressibility and shear moduli are evaluated and discussed. Numerical estimates of the elastic parameters of the polycrystalline LaOFe Pn ceramics are performed for the first time.

First principle calculations have been performed with the purpose to understand the peculiarities of the structural, elastic parameters and electronic properties and interatomic bonding for novel hexagonal carbide (W0.5Al0.5)C in comparison with binary phases WC and Al4C3. The geometries of all phases were optimized and their structural, elastic parameters and theoretical density were established. Besides, we have evaluated the formation energies (Eform) of W0.5Al0.5C for different possible preparation routes (namely for the reactions with the participation of simple substances (metallic W, Al and graphite, binary W or Al carbides and metallic Al and W, or binary W and Al carbides). The results show that the synthesis of the ternary carbide from simple substances is more favorable in comparison with the reactions with participation of W and Al carbides. Moreover, band structures, total and partial densities of states were obtained and analyzed systematically for (W0.5Al0.5)C, WC and Al4C3 phases in comparison with available theoretical and experimental data. The bonding picture in W0.5Al0.5C was described as a mixture of metallic, ionic and covalent contributions with the high anisotropy for the covalent W–C and Al–C bonds, where p–p like Al–C bonds become weaker than p–d like W–C bonds.

Using the full-potential linearized augmented plane-wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential, we studied spin polarization induced by replacement of oxygen atoms by non-magnetic 2p impurities (B, C and N) in non-magnetic cubic SrMO 3 perovskites, where M=Ti, Zr and Sn. The results show that the magnetization may appear because of the spin–split impurity bands inside the energy gap of the insulating SrMO 3 matrix. Large magnetic moments are found for the impurity centers. Smaller magnetic moments are induced on the oxygen atoms around impurities. It is shown that SrTiO 3 :C and SrSnO 3 :C should be magnetic semiconductors while other compounds in this series (SrTiO 3 :B, SrTiO 3 :N and SrZrO 3 :C) are expected to exhibit magnetic half-metallic or pseudo-half-metallic properties.

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 investigate the systematic trends for structural, elastic and electronic properties of cubic SrMO 3 perovskites' family depending on the type of M cations (d 0 : Ti, Zr, d 1 : V, Nb and p: Sn). The optimized lattice parameters, independent elastic constants ( C 11 , C 12 and C 44 ), bulk modulus ( B ), compressibility ( β ), shear modulus ( G ), Young's modulus ( Y ), Poisson's ratio ( ν ), Lame's coefficients ( μ , λ ), as well as band structure, density of states and electron density distributions are obtained and analyzed in comparison with the available theoretical and experimental data. For the first time the numerical estimates of elastic parameters of the polycrystalline SrMO 3 ceramics (in framework of the Voigt–Reuss–Hill approximation) are performed.

First principle 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 were performed to investigate the systematic trends for structural, elastic and electronic properties of the family of superconducting anti-perovskites MCNi3 depending from the type of M cations (M are Mg, Zn and Cd). In result the optimized lattice parameters, independent elastic constants (C11, C12 and C44), bulk modulus B, compressibility β, shear modulus G and tetragonal shear modulus G′ are evaluated. Further, for the first time the numerical estimates of a set of elastic parameters (bulk and shear modulus, Young’s modulus Y, Poisson’s ratio (ν), Lame’s coefficients (μ, λ)) of the polycrystalline superconducting MCNi3 ceramics (in framework of the Voigt–Reuss–Hill approximation) were performed. Besides, the band structures, densities of states (DOS), total and site-projected l-decomposed DOS at the Fermi level, the shapes of the Fermi surfaces, the Sommerfeld’s coefficients and the molar Pauli paramagnetic susceptibility for these anti-perovskites were obtained and analyzed in comparison with the available theoretical and experimental data.

The ab initio VASP–PAW method with the generalized gradient approximation (GGA) has been applied to predict the electronic and magnetic properties of wurtzite-like beryllium oxide (BeO) doped with all 3d metals. Adding of 3d metal ions into BeO transforms the initial non-magnetic insulator BeO into series of magnetic and non-magnetic materials with various functional properties.

A theoretical study of magnetization in non-magnetic cubic perovskite SrTiO3 induced by vacancies in Sr, Ti and oxygen sublattices is presented using the full-potential linear augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) for the exchange-correlation potential. The results show that the oxygen and titanium vacancies lead to the magnetization of non-magnetic perovskite SrTiO3 due to the spin-polarization of valence states for the Ti and O atoms, nearest to these vacancies. In result the insulating SrTiO3 becomes metallic-like with magnetic moments (per cell) 1.30 μB and 3.54 μB for non-stoichiometric SrTiO 3 − δ and SrTi 1 − δ O , respectively. On the contrary, our calculations reveal that for Sr vacancy the non-magnetic state of perovskite is retained, whereas the electronic spectrum of Sr 1 − δ TiO 3 also adopts metallic-like type.

First-principle calculations in the framework of the full-potential linearized-augmented-plane-wave method (FLAPW, as implemented into the WIEN-2k code) have been performed to understand the structural, elastic, cohesive and electronic properties of the meta-stable cubic strontium thorate SrThO 3 . The optimized lattice parameters, elastic parameters, formation energies, densities of states, band structures and charge density distributions are obtained and discussed in comparison with those of cubic SrZrO 3 and ThO 2 .