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Mimimizing a free-energy functional, we investigate the stability of ferroelectric fluid and various solid phases in the Stockmayer system. Our functional is based on the correlations of the isotropic fluid, calculated by integral equations. At the reduced dipole moment m* = 2.0 we found a ferroelectric fluid, but this phase is surpassed by a polarized body-centered tetragonal crystal. Moreover, the system seems to have no liquid phase at all. This behaviour changes when the strength of the isotropic attraction is increased.

The structure of liquid water in contact with a planar wall is calculated for the central force model by which water is modeled as a stoichiometric mixture of partially charged hydrogen and oxygen atoms interacting via effective spherical pair potentials. The density profiles near the wall are obtained from the Wertheim–Lovett–Mou–Buff equation extended to mixtures with coulombic interactions. The correlations in the bulk liquid are calculated by adding bridge functions of appropriate reference hard sphere systems to the hypernetted chain equation. We have obtained structural (stoichiometry, hydrogen bonds) and thermodynamic properties in good agreement with computer simulations. We also expose the water to electric fields due to a surface charge on the wall.

The hard sphere dipole fluid shows an instability towards formation of oriented clusters in the vapour before condensation. The coexistence interface profile is derived from a WDA approximation of the direct correlation function. Integration of the equation for ∇ρ yields also the orientation of the dipoles near the interface.

Investigating the stability of the dipolar hard sphere fluid by localizing the spinodal we found an additional instability for medium and typical vapor densities, an orientational instability with formation of aligned clusters. For liquid densities we find ordinary vaporization. Then we calculate the structure of the liquid–vapor interface of a dipolar hard sphere fluid in the spirit of the weighted density approximation (WDA) using an equation originally derived by Lovett, Mou, and Buff [J. Chem. Phys. 65, 570 (1976)] and Wertheim [J. Chem. Phys. 65, 2377 (1976)]. The surface tension is evaluated on the same level of approximation.

Electronic surface states are introduced from the tight binding approach as well as in the nearly free electron approximation. The localization mechanism and the criteria for Tamm and Shockley states are demonstrated. These concepts yield a new way of estimating the image potential state energies.

For a binary mixture we relate the second order expansion of the grand canonical potential Ω to direct correlation functions and to thermodynamic expressions. The matrix of second functional derivatives of Ω with respect to the particle density fluctuations is diagonalized. The zero of the smallest eigenvalue indicates a phase instability vs particle density fluctuations. The related eigenvector characterizes the instability uniquely. Calculations of correlation functions via the reference hypernetted chain integral equations are performed for a binary mixture of hard core particles with attractive Yukawa interactions; the spinodals are established for different concentrations and different interaction potentials using the calculated correlation functions. Along the spinodal we find a continuous change from predominantly demixing to mainly condensation instabilities.

An exact equation for the pair correlation function of fluids is derived by density functional methods. Comparing this result with the hypernetted chain (HNC) equation we propose a weighted density approximation for the so-called bridge function that improves the ordinary HNC theory. For a hard sphere fluid this method leads to thermodynamically more consistent results than the HNC, Percus-Yevick (PY) and Rogers-Young (RY) approximations. Adding an attractive potential to the hard sphere repulsion we obtain better correlation functions than can be found with the HNC and the reference HNC (RHNC) approximation.

Expressions for the Helmholtz free energy and the chemical potential are derived for fluid mixtures with nonspherical interactions. For the important reference hypernetted chain (RHNC) approximation we can derive explicit formulas. We evaluate the free energy formula for a hard sphere dipole system. The results for the Helmholtz free energy agree well with Monte Carlo simulation.

The structure of an aqueous solution of sodium chloride at a planar electrode is investigated by integral equation techniques. With the central force water model the aqueous electrolyte is modelled as a mixture of sodium and chloride ions and partially charged hydrogen and oxygen atoms interacting via effective spherically symmetric pair potentials. The bulk correlation functions are obtained from the Ornstein-Zernike equation. With the Wertheim-Lovett-Mou-Buff equation we have calculated the density profiles at the uncharged and charged electrode. Steric interactions between the differently sized ions and the ice-like water structure near the electrode dominates the ionic distribution. This model electrolyte also responds differently to opposite charges on the electrode., Comment: Submitted to the Journal of Chemical Physics, REVTeX, 34 pages, 9 figures

For a mixture of hard-sphere dipoles and neutral hard spheres we calculate the correlation functions from integral equations and evaluate the concentration structure factor S cc (k). For large enough dipolar interaction, this structure factor becomes infinite, indicating a demixing phase transition. This instability is also found for charged hard spheres in a dipolar solvent and is the reason for the problems faced previously in investigations of hard-sphere model electrolytes

The absorption spectra of the noble metal atoms Cu, Ag, and Au isolated in Ar, Kr, and Xe matrices have been measured as a function of matrix temperature in the range between 3 K and about 0.4 of the respective matrix triple point temperature. The spectra show a pronounced energy shift of the absorption peaks with temperature which is entirely reversible in well annealed matrices in the above‐given temperature range. These spectra were evaluated by crystal field arguments to obtain more direct information on the matrix influence, which is discussed in terms of difference in level shifts, change in spin–orbit splitting, and crystal field splitting. The results are then explained by a model in which the matrix atoms are treated as clouds of negative charge which introduce a repulsive potential in the region of the metal electrons when the metal atom is squeezed into the matrix cage. The change with temperature in the interaction between metal atom and matrix is discussed in detail. In addition, an unambiguo...

An analytical extension of the unequal size GCS model (URGCS) is presented considering different dielectric constants in the Stern layers and adsorption. Within this model ionic adsorption is treated by Langmuir or Hill-De Boer isotherms. The distance of the adsorption plane from the surface can be varied. A comparison of the calculated differential capacity and concentration dependence of the potential of zero charge with the measurements is given. Characteristic features due to different sizes and to adsorption are discussed.

L'approximation hydrodynamique en optique produit des champs pres de la surface en accord avec ceux qui sont obtenus par le modele microscopique de Feibelman

Angular distributions of photoemission from chemisorption induced states and LEED spectra are calculated for the p (2×2) and the c (2×2) oxygen superstructure on the (001) surface of nickel. The obtained dependence of the photoemission intensity of the polar angle, on the azimuth angle of emission and on the direction of the light beam is discussed using mainly symmetry arguments (selection rules). This kind of analysis is shown to be useful for identifying the orbital symmetry or the symmetry of the adsorbate position without carrying out complicated calculations.

The analysis of spectroscopic ellipsometric data for oxygen adsorption on silver by standard methods leads to implausible results, if the frequency range around ω p of the substrate is investigated. It is shown that taking into account the gradual decrease of the charge density at the metal surface and including the plasma waves in the optical treatment leads to a more consistent description of the experimental results.

The dispersion of plasmons at the surface of a metal and at the interface between two metals is derived by a proper combination of electrodynamics with the hydrodynamic approximation. With a two-step model we discuss the effect of a transition region at the surface of a metal and we so explain recent measurements by Krane and Raether for aluminum.

Electroreflectance spectra of single crystal Ag electrodes have been recorded for various degrees of surface charging. The experimental results obtained with p-polarized light at nonnormal incidence are compared with model calculations for a stratified three layer system. The characteristic spectral features in the vicinity of the volume plasma frequency can be explained only by inclusion of longitudinal plasma waves in the surface layer as well as in the bulk of Ag. By comparison of theory and experiment it is deduced that, at the potential of zero charge, the conduction electron density in the metal surface region is considerably lower than the respective bulk value.

The energy theorem of electrodynamics is cast in a form which yields expressions for the energy current and energy dissipation of a combined field of transverse and longitudinal waves when the longitudinal field is described in the hydrodynamic approximation. This has consequences concerning the boundary conditions for transverse and plasma waves at metal-metal interface and the photoemission yield.

Electroreflectance spectra of Ag and Au single-crystal electrodes and of thin Ag overlayers are analysed and compared with model calculations for a stratified three-layer system. While for s-polarized light the experimentally obtained spectra can be reproduced sufficiently well with classical metal optics, this is not at all the case for p-polarized light. it is demonstrated that the experimental results obtained with p-polarized light in the vicinity of the volume plasma frequency can be explained only by inclusion of longitudinal plasma waves in Ag and Au respectively.

Two oxygen induced peaks are found in the angle resolved UPS using He II (40.8 eV). They are identified by comparing the dependence on the incident angle of light and on the emission direction with calculations. It is shown that anisotropies of the initial states as well as of the final states must be included in calculations in order to get a good agreement.

Bound states and resonances of energy Ec in the atoms of a crystal severely distort the band structure of the crystal in a systematic fashion. The distortions extend throughout the energy range Ec to (c mod H0 mod c), though at the intermediate energies one must look far out into the complex k plane near ki approximately=(c mod H0 mod c)12/. The distortions are expected to be of importance in several surface phenomena.

The existence of surface states in band gaps of a nearly free electron band structure is investigated. While in gaps at the Brillouin zone boundary one finds such a state only for positive potential matrix element, there a surface state always exists for band gaps inside the Brillouin zone.

Electron surface states ond-band metals are investigated by the method of matching the crystal wave function to the outside solution at the surface. On a (100) surface of anfcc structure such a state is found near to the crossover of thes-band and thed-band of the same symmetry. In Ni this state lies 4–5 eV below the Fermi energy, for Cu 5–6 V beloweEF. It explains the density of states anomaly seen in photoemission.

The standard HNC/MSA calculation of the ion distribution fails to describe the packing in a second layer seen in MC calculations. We describe an improved treatment which employs the particle-particle direct correlation function for non-neutral electrolyte compositions as found near the surface.

Iodine adsorbing on a silver (111) surface forms a $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})30\ifmmode^\circ\else\textdegree\fi{}$ structure. The position of the adsorbed atoms within the unit cell of the surface layer has been determined by comparison of the measured curves of intensity versus energy of several low-energy electron diffraction spots with dynamical model calculations.

Matrix isolation spectroscopy is a commonly used tool for the study of reactive species, such as atoms, radicals and molecules (for an introduction see ref. (1–3)). The idea is to isolate the reactive species in an inert matrix, which is rigid enough to prevent diffusion of the isolated entity (and hence prevent successive reactions), but also inert enough not to alter its physical and chemical properties. The species, we are mostly dealing with in this chapter, will be metal atoms which are certainly very reactive and hence are widely studied in matrices.

A local HNC/HNC and a HNC/HNC (hypernetted-chain) treatment of the double layer for 2:1 electrolytes is presented. The local HNC/HNC treatment produces improved structure information about the double layer. For divalent counter-ions, nonmonotonic co-ion profiles and improved charge inversions near the electrode are obtained as well as improved diffuse layer potentials; for monovalent counter-ions, packing layers build up at high surface charges. These are effects due to the treatment of the ionic correlations in non-neutral homogeneous systems with the local composition of the electrolyte in front of the electrode. At zero surface charge, a nonzero surface potential is obtained.

Results are presented of ion density distribution functions, potential of zero charge and differential capacitance calculated for a primitive model electrolyte with hard core ions of unequal size new an electrode surface. The hypernetted chain/mean spherical approximation (HNC/MSA) is used. Comparing with the modified Gouy-Chapman (MGC) theory we emphasize the effects of size asymmetry.

In contrast to the usual three line absorption spectra which are observed when metal atoms with one valence electron are isolated in noble gas matrices, the spectrum of Ag in Xe exhibits two unique features. It shows four absorption lines, and the relative intensities of two lines depend strongly on the matrix temperature. These experimental results are explained by a model which assumes that in addition to the crystal field splitting the Ag P3/2,jz=±3/2 level interacts with a Xe 6s level giving rise to an additional splitting.

By comparison of measured LEED intensity versus energy curves with intensities of dynamical model calculations, the adsorption site of an iodine atom in a √3×√3/30° superstructure on a silver (111) surface has been determined.