Thermodynamic non-additivity in disordered systems with extended phase space

Non-additivity effects in coupled dynamic-stochastic systems are investigated. It is shown that there is a mapping of the replica approach to disordered systems with finite replica indexn on Tsallis non-extensive statistics, if the average thermodynamic entropy of the dynamic subsystem differs from the information entropy for the probability distribution in the stochastic subsystem. The entropic indexq is determined by the entropy difference ΔS. In the case of incomplete information, the entropic indexq=1−n is shown to be related to the degree of lost information.     

Structure of a dipolar fluid in contact with a solid: Adsorption and surface potential

The structure of a dipolar fluid in contact with a solid is investigated using the optimized cluster theory. The solid-liquid interaction is described by an effective one-dimensional potential. The model of a perfect impenetrable wall is dropped. An adsorption potential similar to the non-electrostatic potential appearing in the classical models of the double layer is introduced. We show that the effect of a reasonable adsorption potential is localized in the first monolayer in contact with the solid although the total effect of the solid is non localized in this monolayer. No states of orientation predominate in such a way that we can justify a two- or three-state model. The potential drop g^s(dip) across the interface and the change in the surface Gibbs energy due to the adsorption potential are calculated. An adsorption potential of magnitude 1kT gives g^s(dip) - ?0.6 V. In order to obtain the values of g^s(dip) generally accepted in the literature, no dielectric constant or clusters should be introduced. Because of the competition between the dipolar interaction and the adsorption potential, an increase of the dipole moment does not necessarily increase g^s(dip).     

On the thermodynamics of hard spheres near a soft repulsive wall

We extend the variational method based on the Gibbs-Bogolioubov inequality to the case of fluids against a wall. We investigate the influence of the softness of the wall on the free energy of the system. For small packing fraction we consider a density expansion. The variational results are compared with the exact ones which are given by a direct expansion of the free energy. A comparison between variational and perturbation methods has been done for small packing fraction and also for a case corresponding to the liquid state. The accuracy of the present extension of the variational method to a surface phenomena is found as good as in the bulk fluid. A very simple expression is given for the change on surface tension when we go from the perfect hard wall to soft repulsive wall.     

Incomplete normalization of probability on multifractals

This work is an extension of the incomplete probability theory from the simple case of monofractals previously studied to the more general case of multifractals that can occur in the phase space without equiprobable partition.     

New results from the contact theorem for the charge profile for symmetric electrolytes

In this paper the contact value of the charge profile at a charged interface is presented as the sum of the normal component of the Maxwell electrostatic tensor and a new electrostatic property defined by the integral from the product of the gradient of the electrical potential and the singlet distribution function of coions (ions with sign of the charge equal to that of the interface). On physical arguments, it is conjectured that this new property is a monotonic function of the electrical charge at the wall and is limited by the bulk electrolyte pressure for large electrical charges at the wall. Using the contact theorems for the density and the charge profiles, the exact expressions for the contact values of the profiles of coions and counterions are derived and some related general properties are discussed.     

Negative linear compressibility in confined dilatating systems

The role of a matrix response to a fluid insertion is analyzed in terms of a perturbation theory and Monte Carlo simulations applied to a hard sphere fluid in a slit of fluctuating density-dependent width. It is demonstrated that a coupling of the fluid-slit repulsion, spatial confinement, and the matrix dilatation acts as an effective fluid-fluid attraction, inducing a pseudocritical state with divergent linear compressibility and noncritical density fluctuations. An appropriate combination of the dilatation rate, fluid density, and the slit size leads to the fluid states with negative linear compressibility. It is shown that the switching from positive to negative compressibility is accompanied by an abrupt change in the packing mechanism.     

Structural properties of ionic systems in the restricted primitive model and in a model involving ion-solvent hard core repulsion

Ionic radial distribution functions are calculated in the mean spherical approximation for the restricted primitive model and compared with Monte-Carlo results at high density. They are also calculated when the granularity of the solvent is taken into account.     

Structural rearrangement of solid surfaces due to competing adsorbate-substrate interactions

Employing a generalized lattice gas theory and the Brownian dynamics simulation, we show that the competing displacive interaction in an adsorbate may cause a continuous distortive transition in the underlying substrate. The threshold for the transition is determined by the competition of the substrate rigidity and the quasielastic energy induced by the adsorbate. In the presence of a strong pinning and repulsive lateral interaction, the resulting structure appears as a compromise between the square lattice of the substrate and the hexagonal arrangement of the adsorbate. For hexagonal substrate lattices the simulation demonstrates that various adsorbate structures (from honeycomb lattices to quasicrystalline pentagonal configurations) may be observed, depending on the effective radii of interaction. Due to the long-ranged coupling the substrate may acquire a substructure induced by the adsorbate. This paper represents a generalization of the work published in Phys. Rev. Lett. 81, 3904 (1998).