MgNi2B6 as a new representative of the CeCr2B6 structure type.

Novel ternary phases, (Pd(1-x)Zn(x))(18)(Zn(1-y)Al(y))(86-delta) (0<or=x<or=0.162, 0.056</=y<or=0.088, 0<or=delta<or=4), which adopt a superstructure of the gamma-brass type (called gamma'-brass), have been synthesized from the elements at 1120 K. Single-crystal X-ray structural analysis reveals a phase width (F43m, a=18.0700(3)-18.1600(2) A, Pearson symbols cF400-cF416), which is associated with structural disorder based on both vacancies as well as mixed site occupancies. These structures are constructed of four independent 26-atom gamma-clusters per primitive unit cells and centered at the four special positions A (0, 0, 0), B (1/4, 1/4, 1/4), C (1/2, 1/2, 1/2) and D (3/4, 3/4, 3/4). Two of these, centered at B and C, are completely ordered Pd(4)Zn(22) clusters, whereas the other two, centered at A and D, contain all structural disorder in the system. According to our single-crystal X-ray results, Al substitutions are restricted to the A- and D-centered clusters. Moreover, the outer tetrahedron (OT) site of the 26-atom cluster at D is completely vacant at the Al-rich boundary of these phases. Electronic structure calculations, using the tight-binding linear muffin-tin orbital atomic-spheres approximation (TB-LMTO-ASA) method, on models of these new, ternary gamma'-brass phases indicate that the observed chemical compositions and atomic distributions lead to the presence of a pseudogap at the Fermi level in the electronic density of states curves, which is consistent with the Hume-Rothery interpretation of gamma-brasses, in general.

Tight binding linear muffin-tin orbitals atomic sphere approximation have been used to examine the structural stability, electronic properties, charge density and magnetization of lithium hydride (LiH). In our study, the direct band gap (4.25 eV) detected between the valence bands (especially dominated by hydrogen) and conduction bands implies that LiH is insulating in nature with strong ionic bonds and weak orbitals-hybridization. Furthermore, we noticed that the hydrogen contributed more to the total density of states than the lithium in the complete system, based on the spin polarised partial density of states of H and Li. Because our calculated band gap accords with experiment, the results found in LiH suggest that it is a better choice for optoelectronic devices. The strength of hybridization of orbitals and band gap properties improve energy storage as well.

A universal orthogonal tight-binding (TB) model is developed for transition metals, withspecial emphasis on spin-polarized self-consistent calculations. The parameters of the TBmodel are directly obtained from the ab initio bulk calculations within the linear muffin-tinorbital atomic sphere approximation method, without any fitting. With the environmentaldependence of the Hamiltonian included in the localized structure constants, the TB modelcan be reliably applied to various situations, from periodic bulk structures to smallclusters, for both pure metals and alloys. We have tested the model in spin-polarizedcalculations against ab initio results for small computational cell systems, andapplied the model to study the spin and orbital magnetism of some large clusters.

The electronic structure and band magnetism of disordered ${\mathrm{Fe}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$ and ${\mathrm{Ni}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cu}}_{\mathit{x}}$ bulk alloys and of corresponding disordered overlayers on an fcc Cu(001) substrate were studied by means of the first-principles tight-binding linear muffin-tin orbital coherent potential approximation method. For the Fe-Co system, we found that the composition dependence of the averaged and the local Fe magnetic moments is strongly affected by the dimensionality of the system while the local Co moments remain nearly constant. In the bulk bcc alloys, a nonmonotonic behavior of the averaged magnetization occurs due to the transition from weak to strong ferromagnetism. The averaged magnetization of the random overlayers depends linearly on the composition while the local Fe and Co moments are constant since the strong ferromagnetism is stabilized by the substrate throughout the whole composition range. For the Ni-Cu system, a transition from ferromagnetism to paramagnetism is found both in the bulk fcc alloys and in the overylayers. The ferromagnetism of the overlayers is reduced in comparison to the bulk systems of the same composition. The concentration trends of local densities of states, local numbers of electrons, and work functions are discussed.

We characterize the superconducting state of the carbides YC${}_{2},$ ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Th}}_{x}{\mathrm{C}}_{2},$ and ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{C}}_{2}$ $(0lxl~0.3)$ by means of magnetization and specific-heat measurements. ${\mathrm{YC}}_{2}$ is a superconductor with ${T}_{c}=4.02(5)$ K. Partial substitution with Ca and Th, as well as doping with the strongly pair breaking Gd, reduces the critical temperature. Isothermal magnetization measurements on ${\mathrm{YC}}_{2}$ indicate a superconducting behavior close to the type-I limit with ${B}_{c2}(0)=59(2)$ mT. Specific-heat data of ${\mathrm{YC}}_{2},$ ${\mathrm{Y}}_{0.8}{\mathrm{Th}}_{0.2}{\mathrm{C}}_{2}$, and ${\mathrm{Y}}_{0.9}{\mathrm{Ca}}_{0.1}{\mathrm{C}}_{2}$ are analyzed in terms of weak-coupling BCS theory and the $\ensuremath{\alpha}$ model. The comparison with the model predictions as well as the ${}^{12}\mathrm{C}{/}^{13}$C-isotope effect on ${T}_{c}$ indicate excellent agreement with weak-coupling BCS theory for YC${}_{2}$. A strong dependence of the superconducting properties on the carbon deficiency is observed. We describe high-temperature annealing procedures to optimize the superconducting properties of the samples. Ab initio calculations of the electronic band structure using the tight-binding linear muffin-tin orbital atomic-sphere approximation method are presented and the density of states at the Fermi energy is discussed in view of the experimental Pauli susceptibilities and heat-capacity results.

First-principles electronic structure calculations based on the full-potential linear-muffin-tin-orbital method have been employed to study the contrasting effects of boron and hydrogen on the electronic structure of the L${1}_{2}$ ordered intermetallic ${\mathrm{Ni}}_{3}$Al. The total energy, the site- and l-projected densities of states, and the impurity-induced charge-density characteristics are calculated for various impurity configurations, to investigate the effects of local environment on the electronic structure. Total-energy calculations show that both boron and hydrogen impurities prefer to occupy octahedral interstitial sites that are entirely coordinated by six nickel atoms. Our results suggest that the underlying mechanism of the boron-induced strengthening in ${\mathrm{Ni}}_{3}$Al is the Ni-d and B-p hybridization between the nearest-neighbor nickel and boron sites. This results in an enhancement of the intraplanar metallic bonding between the nickel atoms, an enhancement of interstitial bonding charge, and reduction of the bonding-charge directionality around the Ni atoms on the (001) NiAl planes. In contrast, hydrogen is found to enhance the bonding-charge directionality near some Ni atoms and to reduce the interstitial charge, suggesting that it promotes poor local cohesion. When both boron and hydrogen are present in ${\mathrm{Ni}}_{3}$Al, the dominant changes in the electronic structure are induced by boron and the charge distribution resembles that of ${\mathrm{Ni}}_{3}$Al+B. These results are broadly consistent with the notion of boron as a cohesion enhancer and hydrogen as an embrittler.

Electronic structure and properties of LaNi5 compound from first principles

The crystal and electronic structures, thermodynamic, kinetic, energy and magnetic properties of the thermoelectric material Lu1-xZrxNiSb in the ranges: T=80–400 K, x=0–0.10 were studied. Mechanisms of simultaneous generation of structural defects of acceptor and donor nature are established. It is shown that in the structure of the basic compound LuNiSb there are defects of acceptor nature as a result of vacancies in the crystallographic positions 4a and 4c of Lu and Ni atoms, respectively, which gave rise to acceptor levels (zones) in the band gap εg. Introduction of Zr impurity atoms into the structure of the LuNiSb compound by substitution of Lu atoms in position 4a generates structural defects of donor nature with simultaneous elimination of vacancies in positions 4a and 4c of Lu and Ni atoms, respectively (acceptor levels). The ratio of the concentrations of the available defects of donor and acceptor nature determines the location of the Fermi level εF and the conduction mechanisms in Lu1-xZrxNiSb. The investigated solid solution Lu1-xZrxNiSb is a promising thermoelectric material. Bibl. 15, Fig. 9.

Energy needs are mainly covered by fossil fuels leading to pollutant emissions, mostly responsible for global warming. Among the different possible solutions for the greenhouse-effect reduction, hydrogen has been proposed for energy transportation. Hydrogen can be seen as a clean and efficient future energy carrier. However, the major challenges regarding hydrogen energy is its storage. Of the known methods for hydrogen storage (compressed gas, cryogenic liquid, and metal hydrides), metal hydrides offer the best compromise considering both safety and efficient storage capacity. In this study, a nano structured V–Ni alloy has been synthesized by using high-energy ball milling route. The synthesized alloy is characterized by scanning electron microscope, energy dispersive spectrometer, and X-ray diffraction tools. The mean particle size of this alloy is measured as 12.5 ± 2.90 μm, and the crystallite size is computed as 8.75 ± 0.54 nm. The hydriding–dehydriding characteristics of this alloy are studied using Sievert's principle. The maximum hydrogen absorption in the synthesized V–Ni alloy is measured as 1.92 mass% at only 83°C charging temperature, and release of 1.04 mass% of H2 at discharging temperature of 210°C.

We have developed an approach, based on the linear muffin-tin orbital atomic-sphere approximation (LMTO-ASA) formalism and the recursion method, that allows us to perform first-principles density-functional calculations of electronic structure in real space. Using ${\mathrm{Zr}}_{2}$Fe as a test case, we compare our results with those obtained by using the standard reciprocal-space LMTO-ASA method. The scheme described here can be applied to nonperiodic systems and is also very useful in the study of complex metallic systems with a large number of atoms per unit cell. To illustrate the application of the first-principles real-space approach to a complex system, we calculate the electronic structure for a cluster of amorphous Zr. We use our results to evaluate the distribution of charge transfer among the sites of this randomly packed system. As a first guess we take the potential parameters to be the same for all atoms. The final self-consistent results show charge transfers that are almost an order of magnitude smaller than the ones obtained in the initial run. The major effect of the self-consistent process in this case is to rearrange the center of the bands in order to screen large charge fluctuations. This explains why the parametrized LMTO-ASA approach, where the relative position of the bands is fixed using approximate charge neutrality, works so well when applied to transition-metal alloys.

Graphene, with impressive electronic properties, have high potential in the microelectronic field. However, graphene itself is a zero bandgap material which is not suitable for digital logic gates and its application. Thus, much focus is on graphene nanoribbons (GNRs) that are narrow strips of graphene. During GNRs fabrication process, the occurrence of defects that ultimately change electronic properties of graphene is difficult to avoid. The modelling of GNRs with defects is crucial to study the non-idealities effects. In this work, nearest-neighbor tight-binding (TB) model for GNRs is presented with three main simplifying assumptions. They are utilization of basis function, Hamiltonian operator discretization and plane wave approximation. Two major edges of GNRs, armchair-edged GNRs (AGNRs) and zigzag-edged GNRs (ZGNRs) are explored. With single vacancy (SV) defects, the components within the Hamiltonian operator are transformed due to the disappearance of tight-binding energies around the missing carbon atoms in GNRs. The size of the lattices namely width and length are varied and studied. Non-equilibrium Green.s function (NEGF) formalism is employed to obtain the electronics structure namely band structure and density of states (DOS) and all simulation is implemented in MATLAB. The band structure and DOS plot are then compared between pristine and defected GNRs under varying length and width of GNRs. It is revealed that there are clear distinctions between band structure, numerical DOS and Green\'s function DOS of pristine and defective GNRs.

The electronic structure of pure and Nb doped B2 NiTi have been calculated with the first-principle ultrasoft pseudopotential approach of the plane wave based on the density functional theory aiming at examining the effect of Nb on the electronic structure and bonding characteristic of NiTi. The point defect formation energy calculation results show that the introduction of Nb largely enhances the energy required to form the vacancies and anti-sites of both Ni and Ti sublattice. Furthermore, the calculation results on the partial density of states (PDOS) suggest that the addition of Nb increase the s-s, p-p and d-d electronic interactions between Nb and neighboring Ni and Ti atoms. The electron density of NiTi was also increased with the introduction of Nb. All these Nb-inuced results on electronic structure and bonding characteristic may hamper the hop of Ni and Ti atoms, which may facilitate to improve of oxidation resistance of NiTi intermetallic compound in the experimental findings.

Electronic structures and magnetic properties of ultrathin Ni films $({\mathrm{Ni}}_{n},n=1,4)$ with Cu and Co coverlayers $({\mathrm{Cu}}_{2}/{\mathrm{Ni}}_{4},\mathrm{Co}/{\mathrm{Cu}}_{2}/{\mathrm{Ni}}_{4})$ on the Cu(001) substrate are studied by using the full potential linearized augmented plane wave method with the generalized-gradient approximation for the exchange correlation interactions. The equilibrium structures are determined through their atomic forces. It is found that the spin moments of interfacial Ni atoms are significantly weakened due to the proximity effect from Cu. The Co adlayer in $\mathrm{Co}/{\mathrm{Cu}}_{2}/{\mathrm{Ni}}_{4}/\mathrm{Cu}(001)$ affects the Ni film very slightly due to the screening effects of the Cu layers. The average $3d$ holes increases by about 10% from ${\mathrm{Ni}}_{1}/\mathrm{Cu}(001)$ to ${\mathrm{Ni}}_{4}/\mathrm{Cu}(001).$ In ${\mathrm{Cu}}_{2}/{\mathrm{Ni}}_{4}/\mathrm{Cu}(001),$ the Cu capping layers reduce the average number of $3d$ holes of the Ni atoms by about 7.5% as compared to that in ${\mathrm{Ni}}_{4}/\mathrm{Cu}(001).$ Results are compared to experimental data from recent measurements using magnetic circular dichroism.

Influence of Cr/Zr doping on the electronic structure and hydrogen storage properties of the Mg2Ni (0 1 0) surface: A first principles study

A tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and its nickel(II) picrate (pic) complex, with composition [Ni(Mentb)(DMF)(H2O)](pic)2, have been synthesized and characterized on the basis of elemental analyses, molar conductivities, IR spectra, and UV/Vis measurements. Single-crystal X-ray diffraction revealed that the Ni atom is six-coordinated in a distorted octahedral geometry. In addition, the DNA-binding properties of the ligand Mentb and its Ni(II) complex have been investigated by electronic absorption, fluorescence and viscosity measurements. The experimental results suggest that the ligand and its Ni(II) complex bind to DNA via an intercalation binding mode, and their binding affinity to DNA follows the order of complex&gt;ligand.