Electronic structure and plasticity anomalies of the intermetallic compound Co3Ti

In order to explain the physical causes of the mechanical anomalies of the intermetallic compound Co₃Ti we theoretically determine the dependence of the stacking-fault energy on the composition. The problem of evaluating that energy for Co₃Ti is reduced to a problem of examining the difference of the specific energies of close-packed disordered phases of Co−Ti alloys in the ground state. The energies are calculated within the framework of a model based on the locator method of the electron theory of alloys. The stacking-fault energy is found to become zero in the direct vicinity of the Co₃Ti composition. The possibility that alloying may have an effective influence on that quantity is demonstrated. The density ofd states and the enthalpy of formation of Co−Ti alloys are calculated. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 14–21, June, 1996.     

Electronic structure of the intermetallic compound TiNi

We present the results of self-consistent band structure calculations for the intermetallic compound TiNi in the CsCl structure. The calculated Fermi surface shows nesting features that appear to be consistent with the suggestion of an incommensurate charge density wave.     

Electronic structure and magnetism in transition metal compounds: VNi3, MnPd3 and MoPd3

The electronic structures of VNi₃, MnPd₃ and MoPd₃ are studied in the paramagnetic phase using the method of orthogonalized linear combination of atomic orbitals. The Stoner criterion is applied to predict magnetic ordering in these compounds. VNi₃ has a very low density of states at the Fermi level and therefore does not satisfy the Stoner criterion for magnetic ordering. This is in agreement with the magnetic susceptibility data. Magnetic ordering predicted for MnPd₃ is in agreement with the observed antiferromagnetic phase transition in this compound. The Stoner criterion is not satisfied for MoPd₃ and no experimental data are available for the ordered phase.     

Superconductivity in a molecular metal cluster compound

Compelling evidence for band-type conductivity and even bulk superconductivity below Tc approximately 8 K has been found in (69,71)Ga NMR experiments in crystalline ordered, giant Ga84 cluster compounds. This material appears to represent the first realization of a theoretical model proposed by Friedel in 1992 for superconductivity in ordered arrays of weakly coupled, identical metal nanoparticles.     

Ultrafast electron interactions in metal clusters

The recent extension of time-resolved femtosecond optical techniques to the investigation of the ultrafast electron scattering processes in metal clusters offers the unique possibility to follow their evolution from a bulk to a confined metal. The size dependent results obtained in model materials, the noble metals, are presented, focusing on the impact of the confinement on energy redistribution processes (electron–electron and electron–phonon coupling). Their application to the investigation of the acoustic vibration property of cluster and to the cluster-surrounding matrix energy transfers are also discussed. To cite this article: N. Del Fatti, F. Vallée, C. R. Physique 3 (2002) 365–380.     

Size-dependent electron-electron interactions in metal nanoparticles

The internal thermalization dynamics of the conduction electrons is investigated in silver nanoparticles with radius ranging from 13 to 1.6 nm using a femtosecond IR pump-UV probe absorption saturation technique. A sharp increase of the electron energy exchange rate is demonstrated for nanoparticles smaller than 5 nm. The results are consistent with electron-electron scattering acceleration due to surface induced reduction of the Coulomb interaction screening by the conduction and core electrons.     

Electronic and elastic properties of expanded radialenes carbon nanotubes

The series of expanded radialenes of molecular formulae C_2n H _n and C_3n H _n are obtained by inserting acetylene or diacetylene groups between each pair of methylene units of radialenes C _n H _n . This paper reports on the new theoretical investigation of electronic and elastic properties of some carbon nanotubes based on expanded radialenes with different diameters and with the armchair and zigzag edges Using the ABINIT software package, which is based on the density functional theory (DFT), we found that all studied carbon nanotubes based on expanded radialenes possess metallic behavior. Also, the calculations show that the elastic properties of the nanotubes depend on the form of the rolling up (armchair (m,m) or zigzag (m,0)). The Young’s modulus is slightly smaller for the (m,0) nanotubes and a bit larger for (m,m) nanotubes.     

Electronic structure of metal nanoclusters

The electronic structure and the shape of the K absorption edge for small-sized clusters formed by transition metal atoms (titanium, nickel, and copper) are investigated using the quantum-mechanical multiple scattering method (FEFF8 code) and the molecular mechanics technique. It is shown that the x-ray photoelectron spectra and K x-ray absorption spectra of clusters containing 55 and more atoms are similar to the corresponding experimental spectra of macroscopic samples. The computer simulation of the electronic structure and the shape of the K absorption edge is performed for nanoclusters whose equilibrium geometric shape is determined by the molecular dynamics method.     

Ni基金属间化合物第一性原理研究

稀土(R)-过渡族(T)金属间化合物具有优异的物理和化学性质.本研究考虑电子自旋极化作用,基于第一性原理的全电子投影缀加平面波赝势法理论,采用局域自旋密度近似(LSDA),对Ni₁₃Nd₃B₂金属间化合物进行结构优化,计算体系晶格常数、电子结构和磁性能.结果表明,Ni₁₃Nd₃B₂为带隙很小的金属导体.LSDA近似下体系原子间存在复杂作用类型,Nd原子与近邻Ni,B原子以离子键作用为主,Ni原子与近邻Ni原子间表现共价作用情形.体系存在Nd-Ni铁磁耦合,总磁矩约8.4329μB,主要由Nd原子磁矩提供,自旋极化引起的体系Nd-4f,Ni-3p,Nd-5p电子自旋劈裂为体系表现磁性的根本原因.     

Electronic shell structure in simple metal clusters

The total energies of simple metal clusters (sodium, magnesium, and aluminium) containing up to 100 valence electrons are calculated in the spherical jellium approximation using the local-density-functional scheme. Because of the existence of electronic shell structure, there are abrupt changes in the total energy at certain cluster sizes. This behavior accounts for the peaks or steps found in the mass spectrum of sodium clusters. Predictions for the sizes of magnesium and aluminium clusters which should be abundant in the mass spectra are also discussed.     

Electronic structure of magnetic and non-magnetic substitutional 3d transition metal impurities in germanium

The electronic structure around the ideal 3d transition metal impurities at substitutional site of germanium is calculated self-consistently within the local density formalism. Chemical trend of 3d impuritiy levels caused by the strong p-d hybridization, is revealed in the case of non-magnetic state. The magnetic state of the iron impurity is also presented and the local magnetic moment experienced by iron impurity is calculated to be 3.72μ_B.     

Electronic structure and magnetic properties of the compound CeCuIn

Magnetization, magnetic susceptibility, electrical resistivity, thermoelectric power and X-ray photoemission measurements were performed on a polycrystalline sample of CeCuIn. This compound crystallizes in a hexagonal structure of the ZrNiAl type. The magnetic data indicate that CeCuIn remains paramagnetic down to 1.9 K with a paramagnetic Curie temperature of −13 K and an effective magnetic moment equal to 2.5 μ_B. The electrical resistivity has metallic character, yet in the entire temperature range studied here, it is a strongly nonlinear function of temperature. The temperature dependence of the thermoelectric power is dominated by a small positive maximum near 76 K and a deep negative minimum at about 16 K. Above 150 K the thermopower exhibits a Mott's type behavior. The positive sign of the Seebeck coefficient in this temperature region indicates that the holes are dominant charge and heat carriers. The structure of Ce 3d_5/2 and Ce 3d_3/2 XPS spectra has been interpreted in terms of the Gunnarsson-Schönhammer theory. Three final-state contributions f⁰, f¹ and f² are clearly observed, which exhibit a spin-orbit splitting Δ_SO≈18.7 eV. The appearance of the 3d⁹f⁰ component is a clear evidence of the intermediate valence behavior of Ce. From the intensity ratio I(f⁰)/[I(f⁰)+I(f¹)+I(f²)] the 4f-occupation number is estimated to be 0.95. In turn, the ratio I(f²)/[I(f¹)+I(f²)]=0.08 yields a measure of the hybridization energy that is equal to 45 meV.     

Electronic structure,pairwise interactions and ordering energies in binary f.c.c. transition metal alloys

Effective pair interactions for binary f.c.c. transition metal alloys have been computed using a generalized perturbation method starting from the completely disordered state. Their properties, as a function of interatomic distance, band filling, disorder and concentration are discussed. The ordering energy computed from the pair interactions is succesfully compared, for the Cu₃Autype structure, to the energy derived from the band structure determined by the recursion method.     

Electronic interactions in two-dimensional polymers of the C60 fullerene

The electronic structure of tetragonal and rhombohedral polymers of the C₆₀ fullerene is investigated using x-ray emission spectroscopy. It is found that, compared to the C₆₀ molecular crystals, the formation of intermolecular covalent bonds in two-dimensional layers of the C₆₀ fullerene polymers leads to a broadening of the maxima in the CK _α x-ray emission spectra, a decrease in the density of high-energy states, and an increase in the width of the valence band of the polymer. The experimental data are interpreted by analyzing the results of the calculations performed within the density functional theory for the C₆₀ fullerene cage forming eight and twelve covalent bonds. It is shown that the electronic interactions between C₆₀ molecules in the polymerized layers are provided by two types of molecular orbitals located at energies 0.5–3.0 and ∼5.0 eV below the energy of the Fermi level.     

Electronic theory for the metal-non-metal transition in simple metal alloys

The metal-non-metal transition in liquid alloys such as Cs_1–x Au _x and Li_1–x Pb _x is explained as resulting from concentration dependent electron charge transfer causing short range atomic order and a change from metallic to ionic bonds. Numerical results for the electronic density of states, the electron charge transfer, the free energy of mixing and the volume change are given.     

On the interactions of adatoms on metal surfaces

Pariwise interactions of the adatoms and ions adsorbed on metal surfaces has been investigated with the help of the pole approximation in integral equations of the Lippman-Swinger type. These interactions have been shown to depend mainly both on the type of the metal spectrum and on the electron structure of the adatoms. The theory developed in this paper gives a satisfactory explanation of several facts observed in experiments, especially the longrange oscillating interaction between adatoms.     

Electronic structure and interactions in well-defined coadsorbate layers

A synopsis of results and models for weakly and strongly interacting, well-defined coadsorbate systems is presented. Some experimental examples are given for various adsorbates on Ni(111) representing weak (different N₂ states, Ar/Xe+N₂) as well as strong (N₂+K) interaction. Models for coadsorbate interaction, in particular between molecules (CO, N₂) and alkali atoms, are discussed.