Detection of short-range interactions in combination with tunneling microscopy provides a means for characterizing the chemical nature of surfaces. Results are presented that demonstrate that carbon adsorbed on a rough, polycrystalline Ir surface can be detected on an atomic level.

A single-atom nucleation model is studied in which monomers randomly and irreversibly react with the substrate to become immobile and act as growth nuclei. The reaction kinetics, of first order in monomer density, yields a cluster size distribution that is insensitive to deposition rate and is a decreasing function of cluster size. This matches the experimental behavior of submonolayer Fe inclusions formed by deposition onto room-temperature Cu(100) and observed with the scanning tunneling microscope.

The observable consequences of the dynamic Jahn-Teller effect due to quantum fluctuations between the six degenerate ${\mathit{D}}_{5\mathit{d}}$ polaronic configurations on a singly charged ${\mathrm{C}}_{60}^{\mathrm{-}}$ molecule are considered. The multiphonon infrared-absorption spectrum is calculated taking into account the dynamic symmetry breaking. Some of the Jahn-Teller active (also Raman-active) modes are predicted to be observable as multiphonon overtones in the infrared absorption.

Associated with the ground state of a quantum system, there is a unique stochastic process which, in general, has diffusion and jumping components. This is illustrated in two exact models. The drift and the jumping kernel of the ground-state process may be obtained directly without solving the Schrödinger equation. A method is proposed to extract expectation values and Euclidian correlation functions from a numerical simulation of the process. The method applies equally well to boson and fermion systems, without the sign problem.

The ground-state electronic structure of NiO and MnO has been calculated within the Hartree-Fock approximation using local Gaussian basis sets. For both, a qualitatively correct ground-state electronic structure is obtained in which the wide-band-gap insulating character of these materials is seen to be a result of large on-site Coulomb interactions. The materials are correctly predicted to be antiferromagnetic with the ${\mathit{AF}}_2$ structure. The relative energy differences between various magnetic structures are consistent with the ratio of the Néel temperatures. The structural, elastic, and vibrational properties are in reasonable agreement with available experimental data.

A first-principles technique for calculating accurate equations of state of metals is illustrated with an application to Al. Results for the thermodynamic properties of Al at densities near normal, and at temperatures into the liquid phase, are presented. In contrast to previous calculations by other workers, the present technique makes no use of experimental data. The ab initio procedure begins with electronic-band-structure calculation of the ground-state energy, the elastic constants, and selected short-wavelength phonons. A physically realistic interatomic potential is calibrated by fitting it to the calculated elastic constants and phonons. Ion-motional contributions are computed from quasiharmonic lattice dynamics at low temperatures, and from molecular-dynamics simulations at classical temperatures. Melting is computed from the free energy constructed from these combined results. Very accurate results are obtained for zero-temperature properties and phonon frequencies. The calculated melting temperature of 955 K is within 2.5% of the observed value, a difference comparable to the estimated precision of the calculation. Good results are obtained for two highly sensitive quantities, the entropy change upon melting and the Clapeyron slope. The calculated entropy as a function of temperature is in excellent agreement with experiment for solid and liquid phases. The present procedure can potentially provide reliable values of thermodynamic properties of any metal under extreme conditions where no data are avilable.

The introduction of geometrical complexity into a dielectric structure radically alters the pattern of losses from a passing charged particle. Here we introduce an approach to the problem which is ideally suited to numerical work and to the treatment of complex geometry. We apply the method to losses in colloidal metallic systems where the local juxtaposition of surfaces produces a host of modes and consequent changes in the loss spectrum. We also calculate the ‘‘Smith-Purcell effect,’’ in which a particle passing over a grating may radiate energy into the vacuum. This method is powerful and flexible and will, we trust, open a class of materials to quantitative study.

Here we report the interpretation of all spectral features of Ce ${\mathit{L}}_3$ x-ray-absorption near-edge structure (XANES) of ${\mathrm{CeO}}_2$ over a 40 eV range. The local partial unoccupied density of states in the initial state and in the fully relaxed final state have been calculated by the full multiple-scattering approach. The wave function of the excited electron in the final states of the Ce ${\mathit{L}}_3$-edge XANES spectrum is found to be determined by the multiple-scattering processes in a large size cluster formed by at least 45 atoms. We predict, in good agreement with the experimental data, the crystal-field splitting of 5d states in the final state ${\mathrm{\Delta }}_{\mathit{f}}$=4.0±0.2 eV and its variation from the initial to the final state. The many-body final states for the 2p→5,ɛd transition, arising from the configuration interaction due to mixing of Ce 4f and O 2p valence orbitals, have been calculated taking into account the crystal-field splitting of the 5,ɛd states and they give a full explanation for the low-energy shoulder on the Ce ${\mathit{L}}_3$ x-ray-absorption spectrum white line that was the object of a long-standing discussion. The origin of the pre-edge peak at about 10 eV below the white line maximum is explained as due to transitions at the bottom of the conduction band.

In small samples of ${\mathrm{NbSe}}_3$ the broadband noise of the sliding charge-density wave (CDW) can be partially resolved into two-state and multistate fluctuators, which show strong sensitivity to the bias current and temperature. Explicit violations of detailed balance appear. Near the threshold bias for sliding, intermittent periods of noise occur, indicating that some or all of the sample fluctuates between the pinned and sliding states. The behavior of the discrete fluctuators under a variety of time-dependent bias conditions indicates that some particular configurations are available for the CDW in both sliding and pinned states, but with slower dynamics in the pinned state. The results are consistent with a model in which the noise comes from collective rearrangements of defects in the CDW.

Within the framework of the local-density approximation and the ab initio pseudopotential theory, it is shown that alloying of ${\mathrm{MgH}}_2$ with Li or Al may be described in terms of the rigid-band model. Metallization of insulating ${\mathrm{MgH}}_2$ upon doping with Li or Al should therefore be possible. Doping with Li appears to be more favorable both from a thermodynamic point of view as well as from the objective of obtaining a high density of states at the Fermi level.

We present results of polarized reflectance measurements for unstretched and stretched films of polyaniline in the insulating emeraldine-base (EB) and conducting emeraldine-salt (ES) forms. The reflectance data and the resulting optical conductivity, obtained from a Kramers-Kronig transform of the reflectance data, of unstretched films agree well with optical data reported by S. Stafström et al. [Phys. Rev. Lett. 59, 1464 (1987)]. The stretched films (400% elongation) show significant anisotropy in the reflectance and the other optical constants. The frequency-dependent conductivity in ES exhibits a large shift in oscillator strength to lower energies compared to that of EB and compared to that of unstretched films of ES, which demonstrates delocalization of conduction electrons in the ‘‘polaron band.’’ The dielectric constant of stretched ES indicates that ES is metal-like, with maximum conductivity greater than ten times the dc conductivity. These results indicate that the dc conductivity is likely dominated by interchain processes and that higher values for conductivity are possible.

The results of high-resolution low-energy (1–14 eV)-electron inelastic backscattering experiments on thin solid rare-gas films deposited on a metal substrate have recently been shown to provide an almost direct measurement of the electronic conduction-band density of states (DOS) of those solids. In order to gain more insight into this phenomenon, the variation with film thickness of the backscattered current from solid films of Ar is analyzed with a three-dimensional electron transport model. From this analysis, we determine the electron mean free path (λ) as well as film-vacuum interface terms that characterize the entrance and exit of the electrons. A comparison of the energy dependence of those parameters to that of the calculated DOS of solid argon shows that 1/λ and the DOS are strongly correlated over the whole electron-energy range investigated. In contrast, the interface terms are found to reflect only partly the electronic DOS. It thus appears that the ability of the experimental results to reveal the DOS can be attributed mainly to the role played by the electron mean free path in the reflectivity of the studied films. We also find that electron scatterings in the bulk of the film must be anisotropic (with a preference for forward scattering) to account for the observed distributions of energy losses.

A one-dimensional tight-binding model with correlated disorder is studied. The energy dependence of the localization length and the density of states at different correlation lengths and strengths of the disorder are determined. The results show that the localization length increases with increasing correlation lengths, but in addition, a nonmonotonic energy dependence is found. The energy level statistics is also studied.

We study a two-dimensional (2D) lattice model of forward-directed waves in which the integrated intensity for classical waves (or probability for quantum mechanical particles) is conserved. The model describes the time evolution of a 1D quantum particle in a time-varying potential and also applies to propagation of electromagnetic waves in two dimensions within the parabolic approximation. We present a closed-form solution for propagation in a uniform system. Motivated by recent studies of nonunitary directed models for localized 2D electrons tunneling in a magnetic field, we then address related theoretical questions of how the interference pattern between constrained forward paths in this unitary model is affected by the addition of phases corresponding to such a magnetic field. The behavior is found to depend sensitively on the value of Φ/${\mathrm{\Phi }}_0$, where Φ is flux per plaquette and ${\mathrm{\Phi }}_0$ is the unit of flux quantum. For Φ/${\mathrm{\Phi }}_0$=p/q we find the amplitude to be more collimated the larger the value of q is. We next consider propagation in random forward-scattering media. In particular, the scaling properties associated with the transverse width x of the wave, as a function of its distance t from the point source, are addressed. We find the moments of x to scale with t in a very different way from what is known for either off-lattice unitary or on-lattice nonunitary systems. The scaling of the moments of the probability [${\mathit{P}}^{\mathit{n}}$(x,t)] (or intensity) at a point (x=0,t) is found to be consistent with a simple behavior [${\mathit{P}}^{\mathit{n}}$(0,t)]∼${\mathit{t}}^{\mathrm{-}\mathit{n}/2\mathrm{}}$. Implications for the behavior of one-dimensional lattice quantum particles in a dynamically fluctuating random potential are discussed.

We have implemented an efficient self-consistent Green’s-function technique, based on the tight-binding linear-muffin-tin-orbitals method, for calculating the electronic structure and total energy of a substitutional impurity located either in the bulk or at the surface. The technique makes use of the frozen-core and atomic-sphere approximations but, in addition, includes the dipole contribution to the intersphere potential. Within the concept of complete screening, we identify the surface core-level binding-energy shift with the surface segregation energy of a core-ionized atom and use the Green’s-function impurity technique in a comprehensive study of the surface core-level shifts (SCLSs) of the 4d and 5d transition metals. In those cases, where observed data refer to single crystals, we obtain good agreement with experiment, whereas the calculations typically underestimate the measured shift obtained from a polycrystalline surface. Comparison is made with independent theoretical data for the surface core-level eigenvalue shift, and the much debated role of the so-called initial- and final-state contributions to the SCLS is discussed.

We report on local-spin-density calculations for the ferromagnetic rare-earth metals Gd and Tb using the relativistic first-principles linear-muffin-tin-orbital method in the atomic-sphere approximation. We have used a method which treats simultaneously the localized 4f and the conduction-electron spin magnetism. The 4f magnetic moments are obtained from the Russel-Saunders scheme but the radial 4f spin density is a part of the self-consistent density-functional calculations. The calculated conduction-electron moment for Gd is in very good agreement with the measured value. The calculated de Haas–von Alphen frequencies are in agreement with available data.

Forces on the host-metal atoms surrounding a hydrogen atom at different interstitial positions in palladium and niobium are calculated from first principles in the local-density approximation with a mixed-basis pseudopotential supercell approach. For supercells ${\mathrm{Pd}}_{\mathit{n}}$H (n=1,4,8,16,32) previously reported results are reanalyzed and corrected based on a recently noticed simplification in the computational method. Results are presented for supercells ${\mathrm{Nb}}_{\mathit{n}}$H (n=1,2,4,8,16). In both elements the displacement forces decay dominantly within the range of one lattice constant. The elastic force-dipole tensors are determined from the first-principles forces. The results for octahedral occupation of H in Pd and tetrahedral occupation of H in Nb support the picture of static occupation of distinct interstitial sites.