Flavio Toigo

On skewed ARC plots of impedance of electrodes with an irreversible electrode process

Abstract By a careful analysis of the form of the current implied by the boundary conditions satisfied by the solution of Poissons equation, we generalize previous results and show that irreversible redox processes at a self similarly rough (fractal) electrode give rise to a skewed arc plot in the complex impedance-plane. We also discuss the form of scaling relations obeyed by the current at the electrode to ensure the validity of Ohms law in the solution.

Stochastic growth equations and reparametrization invariance

It is shown that, by imposing reparametrization invariance, one may derive a variety of stochastic equations describing the dynamics of surface growth and identify the physical processes responsible for the various terms. This approach provides a particularly transparent way to obtain continuum growth equations for interfaces. It is straightforward to derive equations which describe the coarse grained evolution of discrete lattice models and analyze their small gradient expansion. In this way, the authors identify the basic mechanisms which lead to the most commonly used growth equations. The advantages of this formulation of growth processes is that it allows one to go beyond the frequently used no-overhang approximation. The reparametrization invariant form also displays explicitly the conservation laws for the specific process and all the symmetries with respect to space-time transformations which are usually lost in the small gradient expansion. Finally, it is observed, that the knowledge of the full equation of motion, beyond the lowest order gradient expansion, might be relevant in problems where the usual perturbative renormalization methods fail.

The binding of alkali atoms to the surfaces of liquid helium and hydrogen

Alkali atoms have been shown previously to have only unstable binding states inside liquid4He. We calculate the equilibrium configurations and binding energies of single alkali atoms near the liquid-vapor interface of4He and3He. A simple interface model is used to predict the surface deformation due to the presence of the atoms. A more realistic density functional model yields somewhat higher energies in the case of4He. For all alkali atoms, we find the surface binding energies to be around 10 to 20 K. A similar analysis with atom-H2 interactions finds that alkali atoms tend to submerge into liquid H2, with the exception of Li.

Ab initio potential energy surfaces of He-CO2 and Ne-CO2 van der Waals complexes

We have calculated ab initio the ground-state potential energy surfaces of Ne-CO2 and He-CO2 van der Waals complexes by using the fourth-order Moller-Plesset perturbation theory with a large basis set containing bond functions. The rigid molecule approximation has been used for CO2. Both complexes have the lowest energy at the T-shaped configuration. In addition, a shallow minimum is found for the linear configuration, with a small barrier connecting the two minima on the potential energy surface, whose height is larger for the lighter noble-gas atom. The implications of these potentials for the wetting behavior of adsorbed films are discussed.

Adsorption of benzene on Si(100) from first principles

Adsorption of benzene on the Si(100) surface is studied from first principles. We find that the most stable configuration is a tetra-

Wetting transitions of 4 He on alkali-metal surfaces from density-functional calculations

\sigma

Systematic trends in van der Waals interactions: Atom–atom and atom–surface cases

-bonded structure characterized by one C-C double bond and four C-Si bonds. A similar structure, obtained by rotating the benzene molecule by 90 degrees, lies slightly higher in energy. However, rather narrow wells on the potential energy surface characterize these adsorption configurations. A benzene molecule impinging on the Si surface is most likely to be adsorbed in one of three different di-

Acetylene on Si(100) from first principles: adsorption geometries, equilibrium coverages, and thermal decomposition

\sigma

ELECTRONIC STRUCTURE AND MAGNETISM OF Y13 CLUSTERS

-bonded, metastable structures, characterized by two C-Si bonds, and eventually converts into the lowest-energy configurations. These results are consistent with recent experiments.

Extended Thomas-Fermi density functional for the unitary Fermi gas

We have studied the wetting properties of He4 adsorbed on the surface of heavy alkali metals by using a non-local free-energy density-functional which describes accurately the surface properties of liquid He4 in the temperature range 0<T<3 K.Our results for He4 on the Cs surface give both the temperature dependence of the contact angle and the wetting temperature in good agreement with the experimental findings. For the He/Rb system we find that a wetting transition on the Rb surface occurs at T=1.4 K, whereas the experiments show either wetting down to T=0 or a wetting transition at T=0.3 K. We suggest that this disagreement is due either to an inaccuracy of the fluid-substrate potential used in our calculations or the consequence of substrate roughness, which is known to affect the Rb surface, and whose effect would be to lower the wetting temperature. The sensitivity of the wetting transition to the He-surface potential are stressed for the He/Rb surface, which may justify the controversial experimental findings for this system.