arXiv subjects

Gabriel Tellez

Publications and source records attributed to Gabriel Tellez.

At least 37 records · Page 2Linked to original sources

arXiv2007

Wigner Surmise For Domain Systems

In random matrix theory, the spacing distribution functions $p^{(n)}(s)$ are well fitted by the Wigner surmise and its generalizations. In this approximation the spacing functions are completely described by the behavior of the exact functions in the limits s->0 and s->infinity. Most non equilibrium systems do not have analytical solutions for the spacing distribution and correlation functions. Because of that, we explore the possibility to use the Wigner surmise approximation in these systems. We found that this approximation provides a first approach to the statistical behavior of complex systems, in particular we use it to find an analytical approximation to the nearest neighbor distribution of the annihilation random walk.

cond-mat.stat-mech↗

arXiv2007

Statistical Behavior Of Domain Systems

We study the statistical behavior of two out of equilibrium systems. The first one is a quasi one-dimensional gas with two species of particles under the action of an external field which drives each species in opposite directions. The second one is a one-dimensional spin system with nearest neighbor interactions also under the influence of an external driving force. Both systems show a dynamical scaling with domain formation. The statistical behavior of these domains is compared with models based on the coalescing random walk and the interacting random walk. We find that the scaling domain size distribution of the gas and the spin systems is well fitted by the Wigner surmise, which lead us to explore a possible connection between these systems and the circular orthogonal ensemble of random matrices. However, the study of the correlation function of the domain edges, show that the statistical behavior of the domains in both gas and spin systems, is not completely well described by circular orthogonal ensemble, nor it is by other models proposed such as the coalescing random walk and the interacting random walk. Nevertheless, we find that a simple model of independent intervals describe more closely the statistical behavior of the domains formed in these systems.

cond-mat.stat-mech↗

arXiv2007

Two-dimensional two-component plasma with adsorbing impurities

We study the behavior of the two-dimensional two-component plasma in the presence of some adsorbing impurities. Using a solvable model, we find analytic expressions for the thermodynamic properties of the plasma such as the $n$-body densities, the grand potential, and the pressure. We specialize in the case where there are one or two adsorbing point impurities in the plasma, and in the case where there are one or two parallel adsorbing lines. In the former case we study the effective interaction between the impurities, due to the charge redistribution around them. The latter case is a model for electrodes with adsorbing sticky sites on their surface.

cond-mat.stat-mech↗

arXiv2007

Renormalized charge in a two-dimensional model of colloidal suspension from hypernetted chain approach

The renormalized charge of a simple two-dimensional model of colloidal suspension was determined by solving the hypernetted chain approximation and Ornstein-Zernike equations. At the infinite dilution limit, the asymptotic behavior of the correlations functions is used to define the effective interactions between the components of the system and these effective interactions were compared to those derived from the Poisson-Boltzmann theory. The results we obtained show that, in contrast to the mean-field theory, the renormalized charge does not saturate, but exhibits a maximum value and then decays monotonically as the bare charge increases. The results also suggest that beyond the counterion layer near to the macroion surface, the ionic cloud is not a diffuse layer which can be handled by means of the linearized theory, as the two-state model claims, but a more complex structure is settled by the correlations between microions.

cond-mat.soft↗

arXiv2007

Charge inversion of colloids in an exactly solvable model

We study a two-dimensional model for a long cylindrical stiff charged macroion immersed in a charge-asymmetric electrolyte with charge ratio +2/-1. The model is integrable and it allows an exact analytical determination of the effective charge of the macroion, which characterizes the electrostatic potential at large distances (compared to the screening length) from the macroion. At at high coulombic coupling, this model predicts charge inversion: for a highly negatively charged macroion, the effective charge could become positive, indicating an overscreening of the macroion by the divalent counterions. By studying the behavior of the coions and counterions density profiles close to the macroion, we show that the counterion condensation threshold is shifted to a lower value in absolute value. This plays an important role in the charge inversion phenomenon.

cond-mat.soft↗

arXiv2006

Equation of state in the fugacity format for the two-dimensional Coulomb gas

We derive the exact general form of the equation of state, in the fugacity format, for the two-dimensional Coulomb gas. Our results are valid in the conducting phase of the Coulomb gas, for temperatures above the Kosterlitz-Thouless transition. The derivation of the equation of state is based on the knowledge of the general form of the short-distance expansion of the correlation functions of the Coulomb gas. We explicitly compute the expansion up to order $O(ζ^6)$ in the activity $ζ$. Our results are in very good agreement with Monte Carlo simulations at very low density.

cond-mat.stat-mech↗

arXiv2006

Finite-Thickness and Charge Relaxation in Double-Layer Interactions

We extend the classical Gouy-Chapman model of two planar parallel interacting double-layers, which is used as a first approximation to describe the force between colloidal particles, by considering the finite-thickness of the colloids. The formation of two additional double layers due to this finite thickness, modifies the interaction force compared to the Gouy-Chapman case, in which the colloids are semi-infinite objects. In this paper we calculate this interaction force and some other size-dependent properties using a mean field level of description, based on the Poisson-Boltzmann (PB) equation. We show that in the case of finite-size colloids, this equation can be set in a closed form depending on the geometrical parameters and on their surface charge. The corresponding linear (Debye-Huckel) theory and the well-known results for semi-infinite colloids are recovered from this formal solution after taking appropriate limits. We use a density functional corresponding to the PB level of description to show how in the case when the total colloidal charge is fixed, it redistribute itself on their surfaces to minimize the energy of the system depending on the afore mentioned parameters. We study how this charge relaxation affects the colloidal interactions.

cond-mat.soft↗

arXiv2005

Onsager-Manning-Oosawa condensation phenomenon and the effect of salt

Making use of results pertaining to Painleve III type equations, we revisit the celebrated Onsager-Manning-Oosawa condensation phenomenon for charged stiff linear polymers, in the mean-field approximation with salt. We obtain analytically the associated critical line charge density, and show that it is severely affected by finite salt effects, whereas previous results focused on the no salt limit. In addition, we obtain explicit expressions for the condensate thickness and the electric potential. The case of asymmetric electrolytes is also briefly addressed.

cond-mat.soft↗

arXiv2005

Short-distance expansion of correlation functions in the charge-symmetric two-dimensional two-component plasma: Exact results

We determine exactly the short-distance leading behavior of the density correlation functions of a two-dimensional two-component charge-symmetric Coulomb gas composed of point particles, in the whole regime of stability where the coulombic coupling $β<2$. More generally, we compute the short-distance behavior of the effective interaction potential between two external arbitrary charges $Q_1$ and $Q_2$ immersed in the plasma, for $β|Q_1|<2$ and $β|Q_2|<2$. We also find the short-distance asymptotics of the density profiles near a single external charge $Q$ immersed in the plasma for $β|Q|<2$.

cond-mat.stat-mech↗

arXiv2005

Guest charges in an electrolyte: renormalized charge, long- and short-distance behavior of the electric potential and density profile

We complement a recent exact study by L. Samaj on the properties of a guest charge $Q$ immersed in a two-dimensional electrolyte with charges $+1/-1$. In particular, we are interested in the behavior of the density profiles and electric potential created by the charge and the electrolyte, and in the determination of the renormalized charge which is obtained from the long-distance asymptotics of the electric potential. In Samaj's previous work, exact results for arbitrary coulombic coupling $β$ were obtained for a system where all the charges are points, provided $βQ<2$ and $β< 2$. Here, we first focus on the mean field situation which we believe describes correctly the limit $β\to 0$ but $βQ$ large. In this limit we can study the case when the guest charge is a hard disk and its charge is above the collapse value $βQ>2$. We compare our results for the renormalized charge with the exact predictions and we test on a solid ground some conjectures of the previous study. Our study shows that the exact formulas obtained by Samaj for the renormalized charge are not valid for $βQ>2$, contrary to a hypothesis put forward by Samaj. We also determine the short-distance asymptotics of the density profiles of the coions and counterions near the guest charge, for arbitrary coulombic coupling. We show that the coion density profile exhibit a change of behavior if the guest charge becomes large enough ($βQ\geq 2-β$). This is interpreted as a first step of the counterion condensation (for large coulombic coupling), the second step taking place at the usual Manning--Oosawa threshold $βQ=2$.

cond-mat.stat-mech↗

arXiv2004

Debye-Huckel theory for two-dimensional Coulomb systems living on a finite surface without boundaries

We study the statistical mechanics of a multicomponent two-dimensional Coulomb gas which lives on a finite surface without boundaries. We formulate the Debye--Huckel theory for such systems, which describes the low-coupling regime. There are several problems, which we address, to properly formulate the Debye--Huckel theory. These problems are related to the fact that the electric potential of a single charge cannot be defined on a finite surface without boundaries. One can only define properly the Coulomb potential created by a globally neutral system of charges. As an application of our formulation, we study, in the Debye--Huckel regime, the thermodynamics of a Coulomb gas living on a sphere of radius $R$. We find, in this example, that the grand potential (times the inverse temperature) has a universal finite-size correction $(1/3) \ln R$. We show that this result is more general: for any arbitrary finite geometry without boundaries, the grand potential has a finite-size correction $(χ/6) \ln R$, with $χ$ the Euler characteristic of the surface and $R^2$ its area.

cond-mat.stat-mech↗

arXiv2004

Description beyond the mean field approximation of an electrolyte confined between two planar metallic electrodes

We study an electrolyte confined in a slab of width $W$ composed of two grounded metallic parallel electrodes. We develop a description of this system in a low coupling regime beyond the mean field (Poisson--Boltzmann) approximation. There are two ways to model the metallic boundaries: as ideal conductors in which the electric potential is zero and it does not fluctuate, or as good conductors in which the average electric potential is zero but the thermal fluctuations of the potential are not zero. This latter model is more realistic. For the ideal conductor model we find that the disjoining pressure is positive behaves as $1/W^3$ for large separations with a prefactor that is universal, i.e. independent of the microscopic constitution of the system. For the good conductor boundaries the disjoining pressure is negative and it has an exponential decay for large $W$. We also compute the density and electric potential profiles inside the electrolyte. These are the same in both models. If the electrolyte is charge asymmetric we find that the system is not locally neutral and that a non-zero potential difference builds up between any electrode and the interior of the system although both electrodes are grounded.

cond-mat.stat-mech↗

arXiv2004

General Considerations on the Finite-Size Corrections for Coulomb Systems in the Debye-Huckel Regime

We study the statistical mechanics of classical Coulomb systems in a low coupling regime (Debye-Huckel regime) in a confined geometry with Dirichlet boundary conditions. We use a method recently developed by the authors which relates the grand partition function of a Coulomb system in a confined geometry with a certain regularization of the determinant of the Laplacian on that geometry with Dirichlet boundary conditions. We study several examples of confining geometry in two and three dimensions and semi-confined geometries where the system is confined only in one or two directions of the space. We also generalize the method to study systems confined in arbitrary geometries with smooth boundary. We find a relation between the expansion for small argument of the heat kernel of the Laplacian and the large-size expansion of the grand potential of the Coulomb system. This allow us to find the finite-size expansion of the grand potential of the system in general. We recover known results for the bulk grand potential (in two and three dimensions) and the surface tension (for two dimensional systems). We find the surface tension for three dimensional systems. For two dimensional systems our general calculation of the finite-size expansion gives a proof of the existence a universal logarithmic finite-size correction predicted some time ago, at least in the low coupling regime. For three dimensional systems we obtain a prediction for the perimeter correction to the grand potential of a confined system.

cond-mat.stat-mech↗

arXiv2004

Non-linear screening of spherical and cylindrical colloids: the case of 1:2 and 2:1 electrolytes

From a multiple scale analysis, we find an analytic solution of spherical and cylindrical Poisson-Boltzmann theory for both a 1:2 (monovalent co-ions, divalent counter-ions) and a 2:1 (reversed situation) electrolyte. Our approach consists in an expansion in powers of rescaled curvature $1/(κa)$, where $a$ is the colloidal radius and $1/κ$ the Debye length of the electrolytic solution. A systematic comparison with the full numerical solution of the problem shows that for cylinders and spheres, our results are accurate as soon as $κa>1$. We also report an unusual overshooting effect where the colloidal effective charge is larger than the bare one.

cond-mat.soft↗

arXiv2003

Confined Coulomb systems with absorbing boundaries: the two-dimensional two-component plasma

Using a solvable model, the two-dimensional two-component plasma, we study a Coulomb gas confined in a disk and in an annulus with boundaries that can adsorb some of the negative particles of the system. We obtain explicit analytic expressions for the grand potential, the pressure and the density profiles of the system. By studying the behavior of the disjoining pressure we find that without the adsorbing boundaries the system is naturally unstable, while with attractive boundaries the system is stable because of a positive contribution from the surface tension to the disjoining pressure. The results for the density profiles show the formation of a positive layer near the boundary that screens the adsorbed negative particles, a typical behavior in charged systems. We also compute the adsorbed charge on the boundary and show that it satisfies a certain number of relations, in particular an electro-neutrality sum rule.

cond-mat.stat-mech↗

arXiv2003

Finite-Size Corrections for Coulomb Systems in the Debye-Huckel Regime

It has been argued that for a finite two-dimensional classical Coulomb system of characteristic size $R$, in its conducting phase, as $R\to \infty $ the total free energy (times the inverse temperature $β$) admits an expansion of the form: $βF=AR^{2}+BR+{1/6}χ\ln R,$ where $χ$ is the Euler characteristic of the manifold where the system lives. The first two terms represent the bulk free energy and the surface free energy respectively. The coefficients $A$ and $B$ are non-universal but the coefficient of $\ln R$ is universal: it does not depend on the detail of the microscopic constitution of the system (particle densities, temperature, etc...). By doing the usual Legendre transform this universal finite-size correction is also present in the grand potential. The explicit form of the expansion has been checked for some exactly solvable models for a special value of the coulombic coupling. In this paper we present a method to obtain these finite-size corrections at the Debye--Hückel regime. It is based on the sine-Gordon field theory to find an expression for the grand canonical partition function in terms of the spectrum of the Laplace operator. As examples we find explicitly the grand potential expansion for a Coulomb system confined in a disk and in an annulus with ideal conductor walls.

cond-mat.stat-mech↗

arXiv2003

A density functional theory study of electric potential saturation: planar geometry

We investigate the possibility of electrostatic potential saturation, which may lead to the phenomenon of effective charge saturation. The system under study is a uniformly charged infinite plane immersed in an arbitrary electrolyte made up of several micro-species. To describe the electric double layer, we use a generic density functional theory in which the local micro-ionic density profiles are arbitrary functions of the local electrostatic potential. A necessary and sufficient condition is obtained for saturation, whereby the electrostatic potential created by the plane becomes independent of its bare charge, provided the latter is large enough.

cond-mat.soft↗

arXiv2002

On the bulk modulus of the cell model of charged macromolecules suspensions

We study theoretically the bulk modulus (inverse of the compressibility) of a suspension of charged objects (macro-ions), making use of a cell model to account for the finite density of macro-ions. The diffuse layer of charged micro-species around a macro-ion is described by a generic local density functional theory. Within this general framework, we obtain the condition for a positive bulk modulus, which is fulfilled by several proposals made in the literature and rules out the possibility of a critical point. We show that a sufficient condition for a positive compressibility also ensures that the same theory produces repulsive effective pair potentials.

cond-mat.soft↗