We present local-density calculations of surface segregation profiles in a random ${\mathrm{Pt}}_{50}$${\mathrm{Ni}}_{50}$ alloy. We find that the concentration profiles of the three low-index surfaces oscillate and that the two most closely packed surfaces, i.e., (111) and (100), are enriched by Pt while Ni is found to segregate to the surface of the (110) face. These results may be explained in terms of a competition between the tendency of Pt to segregate towards the two first surface layers at the (110) face and the tendency to form a structure of alternating Pt and Ni layers.

We propose a method of analysis that allows indirect determination of magnetoelastic coupling coefficients for thin magnetic films. The method is based on a general phenomenological equation describing the dependence of the effective magnetic anisotropy energy density on film thickness for a thin cubic ferromagnetic film sandwiched between two nonmagnetic layers of the same material. We show that by fitting the measured effective anisotropy energy density with this equation using independently measured elastic strain in the film and the saturation magnetization ${\mathit{M}}_{\mathit{s}}$, we can extract the Néel surface magnetic anisotropy energy density ${\mathit{K}}^{\mathit{s}}$ and either of the surface magnetoelastic coupling coefficients ${\mathit{B}}_1^{\mathit{s}}$ or ${\mathit{B}}_2^{\mathit{s}}$ depending on the film orientation. The model is applied to published data for fcc Co/Cu(111) superlattices. We find that ${\mathit{B}}_2^{\mathit{s}}$=-23.5 erg/${\mathrm{cm}}^2$ and ${\mathit{K}}^{\mathit{s}}$(Co/Cu)(111)=+0.47 erg/${\mathrm{cm}}^2$. While such large values of ${\mathit{B}}^{\mathit{s}}$ relative to ${\mathit{K}}^{\mathit{s}}$ are surprising, recent direct measurements of ${\mathit{B}}^{\mathit{s}}$ in polycrystalline Ni films show these values to be reasonable.

Electrical transport is measured for a crystal and polycrystalline samples of ${\mathrm{Ni}}_3$${\mathrm{S}}_2$. The samples display metallic behavior with the relative resistance decreasing by more than two orders of magnitude upon cooling from 300 to 4.5 K. Low-temperature heat-capacity data are obtained by the quasiadiabatic heat-pulse method. The electronic-heat-capacity constant is determined to be 2.7 mJ/${\mathrm{K}}^2$ ${\mathrm{mol}}_{\mathrm{Ni}}$. The magnetic measurements on single-crystal and polycrystalline samples yield a mass magnetic susceptibility of 0.3×${10}^{\mathrm{-}6}$ emu/g [0.4×${10}^{\mathrm{-}8}$ ${\mathrm{m}}^3$/g], which is essentially temperature independent. The Pauli paramagnetic susceptibility is determined to be 5.0×${10}^{\mathrm{-}5}$ emu/${\mathrm{mol}}_{\mathrm{Ni}}$ [6.3×${10}^{\mathrm{-}10}$ ${\mathrm{m}}^3$/${\mathrm{mol}}_{\mathrm{Ni}}$], corrected for the underlying diamagnetism. Results of the electrical transport, magnetic, and heat-capacity measurements are used to characterize the electronic structure. Application of the standard theory of electron-correlation phenomena shows that ${\mathrm{Ni}}_3$${\mathrm{S}}_2$ may be categorized as a good metallic conductor for which magnetic instabilities and electronic interactions are of marginal importance.

We describe a theoretical scheme for the determination of quasiparticle spectra starting from the energy band structure of a metal and treating the on-site Hubbard repulsion beyond the mean-field theory. The method relies upon an expansion of the many-body states in terms of uncorrelated states with a different number of electron-hole pairs. By truncating the expansion to include configurations with one or two pairs one can achieve approximate expressions of the electron and hole self-energies. The interparticle scattering matrices appearing in such expressions are conveniently calculated using the Faddeev approach. Calculations performed for a constant density of states allow us to illustrate the role of three-body correlations in the metal-insulator transitions.

First principles pseudopotential calculations with a plane wave basis set are performed for a variety of real and hypothetical Al-rich structures in the Al-Co system. The technical issues arising in the application of the plane wave pseudopotential method to these compounds, specifically the transferability and the energy convergence of the pseudopotentials, the broadening schemes for finite k-point sampling, and the implementation of the conjugate gradients algorithm for metallic systems, are discussed. The structural properties of fcc Al and AlCo in the CsCl (B2) structure are studied in detail, and found to be in good agreement with experiment and linear augmented-plane-wave method calculations. Results from first principles total energy calculations for the full set of structures considered are discussed in connection with recent pair potential calculations, trends in the electronic density of states, and the structural energetics of these intermetallic compounds, closely related to quasicrystals.

We report an ab initio calculation of the crystal-field parameters ${\mathit{b}}_{\mathit{l}\mathit{m}}$ of rare-earth ions in intermetallic R${\mathrm{Ni}}_5$ compounds. The parameter with given l and m is calculated by integrating the product of the aspherical (l,m) component of the crystal potential and the radial density of 4f electrons of the rare-earth ion. The potential results from the self-consistent calculation of the electronic structure of R${\mathrm{Ni}}_5$ using the full-potential linear augmented plane-wave method, while the density of the 4f electrons is taken from a local-density approximation–self-interaction correction atomic calculation. The calculated parameters are then compared with parameters obtained by other authors from the analysis of experimental results.

A tight-binding method is applied to study the electronic structure of the orthorhombic and tetragonal phases of pure ${\mathrm{As}}_2$${\mathrm{O}}_5$ as well as its hydrated crystalline compounds ${\mathrm{As}}_2$${\mathrm{O}}_5$⋅5/${3\mathrm{H}}_2$O and ${\mathrm{As}}_2$${\mathrm{O}}_5$⋅${4\mathrm{H}}_2$O. From the calculated density of states we give the contribution of the atomic states to the x-ray photoemission valence-band spectrum. As atoms in tetrahedral environments exhibit a characteristic peak which is not found for As in octahedral coordination. In the case of hydrated oxides we predict a smaller valence-band width than in the pure oxides.

X-ray and ultraviolet photoelectron spectra of the valence band and core levels of ${\mathrm{CrCl}}_3$ and α-${\mathrm{RuCl}}_3$ crystals have been performed in order to study their electronic structure. It is found that the 3d and 4d states of the transition metal and the 3p states of the chlorine contribute to the valence-band structure. The valence band consists of overlapping Cr 3d and Cl 3p states in ${\mathrm{CrCl}}_3$, while a narrow Ru 4d band is separated by 2–2.5 eV from the top of the Cl 3p valence states in ${\mathrm{RuCl}}_3$. Photoemission, photoconductivity, and optical spectra indicate that in ${\mathrm{CrCl}}_3$ and ${\mathrm{RuCl}}_3$ the energy gap involves d-d Coulomb and exchange interactions on the transition-metal atom. On this basis, the main 3d- and 4d-emission structures are assigned to unscreened 3${\mathit{d}}^2$ and 4${\mathit{d}}^4$ hole states within the framework of the Mott-Hubbard model.

The residual electrical dc resistivity of the transition-metal-alloy system Cu-Pt is evaluated by making use of the relativistic version of the Korringa-Kohn-Rostoker–coherent potential approximation and the one-electron Kubo-Greenwood formula for disordered systems. Starting from the results of a previous calculation the influence of truncation of the angular momentum expansion, the effects of self-consistency of the alloy potential, the importance of vertex corrections, and the difference between the nonrelativistic and the relativistic current operator are examined.

We study here an extension of the periodic Anderson model by considering finite f-band width. A variational method recently developed by us has been used to study the temperature dependence of the electronic specific heat C and the thermoelectric power Q for different values of the f-band width. We find that as the f-band width increases, the low-temperature peak in C becomes broader and shifts toward the high-temperature region. While the low-temperature peak in Q becomes sharper and shifts toward the low-temperature region and disappears for still larger values of the f-band width.

A random two-dimensional checkerboard of squares of conductivities 1 and δ in proportions p and 1-p is considered. Classical duality implies that the effective conductivity obeys ${\mathrm{\sigma }}^{\mathrm{*}}$= √δ at p=1/2. It is rigorously found here that to leading order as δ→0, this exact result holds for all p in the interval (1-${\mathit{p}}_{\mathit{c}}$,${\mathit{p}}_{\mathit{c}}$), where ${\mathit{p}}_{\mathit{c}}$≊0.59 is the site percolation probability, not just at p=1/2. In particular, ${\mathrm{\sigma }}^{\mathrm{*}}$(p,δ)= √δ +O(δ), as δ→0, which is argued to hold for complex δ as well. The analysis is based on the identification of a ‘‘symmetric’’ backbone, which is statistically invariant under interchange of the components for any p∈(1-${\mathit{p}}_{\mathit{c}}$,${\mathit{p}}_{\mathit{c}}$), like the entire checkerboard at p=1/2. This backbone is defined in terms of ‘‘choke points’’ for the current, which have been observed in an experiment.

We report the crystal and electronic band structures at 295 K and measurements of temperature-dependent magnetic susceptibility, electron paramagnetic resonance, optical reflectivity, conductivity, and thermopower for two copper tetrahalide salts of bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF), (BEDT-TTF${)}_3$${\mathrm{CuBr}}_4$ and (BEDT-TTF${)}_3$${\mathrm{CuCl}}_2$${\mathrm{Br}}_2$. The two salts are isostructural with layers of BEDT-TTF having charges of 0 and +e separated by layers of pseudo-square-planar tetrahalides of copper (II). At ambient pressure these salts show conductivities near 1 S ${\mathrm{cm}}^{\mathrm{-}1}$, and the magnetic properties indicate coupled localized spins present on both BEDT-TTF and the ${\mathit{d}}^9$ copper layers. At 60 K, there is a discontinuous drop in susceptibility, a sharpening of the electron paramagnetic resonance linewidth, and an increase in g value that we attribute to the loss of the contribution from the BEDT-TTF sheets. This may be associated with a Jahn-Teller distortion of the planar copper complexes. Below the transition temperature the susceptibility can be fitted to a quadratic layer antiferromagnet with J=15 K (${\mathrm{CuBr}}_4$) and 8 K (${\mathrm{CuCl}}_2$${\mathrm{Br}}_2$) and one spin per formula unit. Under pressure there is a very rapid increase in conductivity, to 500 S/cm at 24 kbar, the largest increase of conductivity under pressure in any molecular solid yet studied. There is a sharp transition from metal to insulator at temperatures rising to 111 K near 5 kbar, and falling to 80 K at 20 kbar. We consider that these salts are nearly metallic at ambient pressure, with strongly enhanced susceptibilities, but are brought to a fully metallic state under pressure as a result of increased intermolecular contacts.

We have calculated the anisotropic dielectric function for PdO and PtO using the linear-muffin-tin-orbital–atom-sphere-approximation method. The optical matrix elements are explicitly included in the calculations and we find that they play a significant role in determining the shape of the frequency dependence of the dielectric function and its anisotropy. Our calculated dielectric functions for PdO are compared with the recent data of Weber et al. The agreement is good although the calculations show more features than are observed experimentally and give a band gap that is too small by about 0.6 eV. For PtO there are no experimental data available. We conclude that for these two transition-metal monoxides an itinerant description of the d states is appropriate.

We study the spin-exchange scattering amplitude at two-loop (1/${\mathit{N}}^2$) order for the infinite-U Hubbard model away from the metal-insulator filling, with finite electron charge, for which a well-defined 1/N expansion is possible, the mean-field level being equivalent to Gutzwiller enhanced quasiparticles. We find a positive spin-exchange Landau parameter which suggests that the spin-density fluctuations show a well-defined collective mode near the metal-insulator filling. This behavior is interpreted as paralleling the spin and charge separation in the Luttinger liquid.

${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR measurements on single crystals of (fluoranthenyl${)}_2$${\mathrm{PF}}_6$ at variable temperatures and for different orientations of the crystals with respect to the external field reveal strongly temperature-dependent Knight-shift anisotropies. Hyperfine-interaction tensors for the different carbon sites of the fluoranthene molecule were determined and are compared with molecular-orbital-type calculations. The temperature dependence of the paramagnetic spin susceptibility was determined through the metal-insulator transition. The spectra exhibit clearly a structural, as well as a metal-insulator, phase transition at and below 200 K. A detailed analysis of the temperature-dependent shift data leads to the determination of the temperature-dependent order parameter for both transitions.

We study the electronic spectrum for doped electronic states in the orientationally disordered ${\mathit{M}}_3$${\mathrm{C}}_{60}$ fullerides. Momentum-resolved Green’s functions are calculated within a cluster-Bethe-lattice model and compared with results from calculations on periodically repeated supercells containing quenched orientational disorder. Despite the relatively strong scattering from orientational fluctuations, the electronic states near the Fermi energy are well described by propagating states characterized by an effective Bloch wave vector and a mean free path l≊20 Å. The effective Fermi surface is calculated in this model. This differs from that previously calculated for the orientationally ordered crystal, but is relatively well described within a disorder-averaged virtual-crystal Hamiltonian, which we derive.