arXiv subjects

Miguel Hoyuelos

Publications and source records attributed to Miguel Hoyuelos.

At least 19 recordsLinked to original sources

arXiv2026

A general thermodynamic approach for diffusion on a lattice

This work presents a general thermodynamic approach to describe particle diffusion on a lattice, a model used to study transport processes in solids and on surfaces. By treating each lattice site as an open thermodynamic system, the effects of microscopic particle interactions are represented through the chemical potential. A fundamental relationship between the Onsager matrix ($L$) and its ideal-system counterpart ($L_\text{id}$, where interactions are neglected) using the determinant of the covariance matrix is demonstrated. This framework allows for the calculation of transport coefficients using the combination of their ideal values and thermodynamic properties. The general result is successfully applied to reproduce the Darken equation for substitutional diffusion in solids and to derive the non-diagonal diffusion matrix of the Zhdanov model for surface diffusion of Langmuir particles. In the last case, analytical predictions are further validated through numerical simulations across various interaction potentials.

cond-mat.stat-mech↗

arXiv2026

Transport coefficients in hard-sphere fluids: thermodynamic versus kinetic descriptions

A thermodynamic theory for transport coefficients in hard-sphere fluids is developed from a general expression for the Onsager matrix. The theory predicts the ratio $σ/σ_{\rm id}$, where $σ$ is a transport coefficient and $σ_{\rm id}$ denotes its dilute-gas value. This ratio depends exclusively on equilibrium thermodynamic properties and can therefore be computed directly from the equation of state. Compact expressions are obtained for the thermal conductivity, viscosity, and self-diffusion coefficient. These expressions quantitatively reproduce simulation data over almost the entire fluid range and, in the case of self-diffusion, significantly improve upon the predictions of Enskog kinetic theory. The results demonstrate that transport coefficients can be accurately described within a purely thermodynamic framework.

cond-mat.stat-mech↗

arXiv2025

A thermodynamic framework for the thermal conductivity of dense fluids

A thermodynamic framework that predicts the thermal conductivity $λ$ of simple fluids beyond the dilute-gas limit is introduced. By generalizing the transition-rate approach of particles on a lattice to conserved quantities in continuous space, an expression for the ratio $λ/λ_{\rm id}$ is derived, where $λ_{\rm id}$ is the dilute-gas value; the ratio depends solely on equilibrium thermodynamic properties and is therefore directly computable from any equation of state. The resulting formula quantitatively reproduces simulation data for hard spheres throughout almost the entire fluid range, and captures the behavior of Lennard-Jones fluids in the supercritical region where thermodynamic fluctuations remain moderate. Comparison with experimental data for argon, reported by other authors, also shows good agreement. These results provide evidence that transport coefficients of dense fluids can be expressed as their dilute-gas values multiplied by a universal function of equilibrium thermodynamic properties.

cond-mat.stat-mech↗

arXiv2025

Transport with noise in dilute gases: Effect of Langevin thermostat on transport coefficients

In dilute gases, transport properties such as the thermal conductivity, self-diffusion, and viscosity are significantly affected by interatomic collisions, which are determined by the potential form. This study explores these transport properties in the presence of a Langevin thermostat in systems where particles interact through various potentials, including soft-core and hard-core potentials, both with and without an attractive region. Using molecular dynamics simulations and a theoretical approach based on an analogy with an electric circuit (Ohm's law), we derived and compared the transport coefficients across these interatomic potentials for different couplings with the thermostat. The transport coefficients were obtained by considering the thermostat as a resistance in a series circuit.

cond-mat.stat-mech↗

arXiv2025

Physical meaning of nonextensive term in Massieu functions

In this paper we explore the significance of nonextensive terms in Massieu functions. Finite-size effects are in many cases dominated by a term proportional to the surface area. Nevertheless, in numerical simulations of finite systems with periodic boundary conditions, the nonextensive term can become the dominant correction to Massieu functions. This paper presents a general approach linking these nonextensive terms to thermodynamic fluctuations, demonstrating that equations of state inherently encode this information. Numerical simulations corroborate our results. The examples used are hard sphere and hard disk fluids and a one-dimensional spin lattice, emphasizing the applicability of the results across different classes of systems.

cond-mat.stat-mech↗

arXiv2023

Self-diffusion coefficient as a function of the thermodynamic factor

Much effort has been put into developing theories for dense fluids, as a result of these efforts many theories work for a certain type of particle or in a certain concentration regime. Rosenfeld proposed a dependence of the self-diffusion coefficient on the excess entropy. Our proposal is similar to Rosenfeld's in that it also attempts to describe diffusion in terms of a thermodynamic function but, instead of the excess entropy, we use the thermodynamic factor, or the excess chemical potential. Simulations were taken for hard spheres and our model was fitted with two free parameters. Simulations were then carried out for a Lennard Jones gas and our model correctly described the new data with the value of the free parameters that we had obtained for hard spheres. This is a feature of our model that we wish to emphasize, since the usual situation is that parameters have to be re-adjusted for different interaction potentials. An experimental xenon self-diffusion data set was used as an example where the model can be applied, especially in the high-density regime.

cond-mat.stat-mech↗

arXiv2023

Dark energy based on exotic statistics

Dark energy is an elusive concept, which has been introduced two decades ago in order to make the acceleration of the universe a comprehensible phenomenon. However, the nature of this energy is far from being understood, both from a fundamental as well as an observational way. In this work we study cosmological consequences of the existence of particles (which we called ``ewkons'' in a previous work) which are quasi distinguishable, obey unorthodox statistics, and have an equation of state similar to many existent dark energy candidates (including negative relation between pressure and energy density). We find an effective scalar field description of this ewkon fluid, and obtain cosmological solutions for the dark energy dominated epoch. This can be considered as a one-parameter class of dark energy models.

hep-ph↗

arXiv2022

Diffusion on a lattice: transition rates, interactions and memory effects

We analyze diffusion of particles on a two dimensional square lattice. Each lattice site contains an arbitrary number of particles. Interactions affect particles only in the same site, and are macroscopically represented by the excess chemical potential. In a recent work, a general expression for transition rates between neighboring cells as functions of the excess chemical potential was derived. With transition rates, the mean field tracer diffusivity, $D^\text{MF}$, is immediately obtained. The tracer diffusivity, $D = D^\text{MF} f$, contains the correlation factor $f$, representing memory effects. An analysis of the joint probability of having given numbers of particles at different sites when a force is applied to a tagged particle allows an approximate expression for $f$ to be derived. The expression is applied to soft core interaction (different values for the maximum number of particles in a site are considered) and extended hard core.

cond-mat.stat-mech↗

arXiv2021

Application of the Widom insertion formula to transition rates in a lattice

We consider diffusion of particles on a lattice in the so-called dynamical mean-field regime (memory effects are neglected). Interactions are local, that is, only among particles at the same lattice site. It is shown that a statistical mechanics analysis that combines detailed balance and Widom's insertion formula allows for the derivation of an expression for transition rates in terms of the excess chemical potential. The rates reproduce the known dependence of self-diffusivity as the inverse of the thermodynamic factor. Soft-core interactions and general forms of the excess chemical potential (linear, quadratic, and cubic with the density) are considered.

cond-mat.stat-mech↗

arXiv2021

Transition state theory applied to self-diffusion of hard spheres

A description in terms of transition rates among cells is used to analyze self-diffusion of hard spheres in the fluid phase. Cell size is assumed much larger than the mean free path. Transition state theory is used to obtain an equation that matches numerical results previously obtained by other authors. Two regimes are identified. For small packing fraction $ξ$, diffusion is limited by free volume; and, for large $ξ$, diffusion is limited by velocity autocorrelation. The expressions obtained in each regime do not require adjustable parameters.

cond-mat.stat-mech↗

arXiv2021

Out-of-equilibrium Monte Carlo simulations of a classical gas with Bose-Einstein statistics

Algorithms to determine transition probabilities in Monte Carlo simulations are tested using a system of classical particles with effective interactions which reproduce Bose-Einstein statistics. The system is appropriate for testing different Monte Carlo simulation methods in out-of-equilibrium situations since non equivalent results are produced. We compare mobility numerical results obtained with transition probabilities derived from Glauber and Metropolis algorithms. Then, we compare these with a recent method, the interpolation algorithm, appropriate for non-equilibrium systems in homogeneous substrata and without phase transitions. The results of mobility obtained from the interpolation algorithm are qualitatively verified with molecular dynamics simulations for low concentrations.

cond-mat.stat-mech↗

arXiv2019

Diffusion in binary mixtures: an analysis of the dependence on the thermodynamic factor

We study the diffusion process in binary mixtures using transition probabilities that depend on a mean-field potential. This approach reproduces the Darken equation, a relationship between the intrinsic and the tracer diffusion coefficients, $D_A$ and $D_A^*$, through the thermodynamic factor $Φ$ (a function of the derivative of the activity coefficient against molar fraction). The mean-field approach allows us to go beyond the Darken equation and separately specify the dependence of $D_A$ and $D_A^*$ on the thermodynamic factor. We obtain that $Φ$ appears in the expression for $D_A^*$, but the intrinsic diffusivity $D_A$ turns out to be independent of $Φ$. Experimental results taken from the literature on diffusion in metal alloys are consistent with this theoretical prediction.

cond-mat.stat-mech↗

arXiv2019

From diffusion experiments to mean-field theory simulations and back

Using previous experimental data of diffusion in metallic alloys, we obtain real values for an interpolation parameter introduced in a mean-field theory for diffusion with interaction. Values of order 1 were found as expected, finding relevance for this quantity as a way to better understand the underlying dynamics of diffusion processes. Furthermore, using this theory, we are able to estimate the values of the mean-field potential from experimental data. As a final test, we reobtain, with all this information as an input to our simulations, the diffusion coefficient in the studied metallic alloys. Therefore, the method provides appropriate transition probabilities to perform Monte Carlo simulations that correctly describe the out of equilibrium behavior.

physics.chem-ph↗

arXiv2017

From creation and annihilation operators to statistics

A procedure to derive the partition function of non-interacting particles with exotic or intermediate statistics is presented. The partition function is directly related to the associated creation and annihilation operators that obey some specific commutation or anti-commutation relations. The cases of Gentile statistics, quons, Polychronakos statistics, and ewkons are considered. Ewkons statistics was recently derived from the assumption of free diffusion in energy space (Phys. Rev. E 94, 062115, 2016); an ideal gas of ewkons has negative pressure, a feature that makes them suitable for the description of dark energy.

cond-mat.stat-mech↗

arXiv2017

Invited review: Fluctuation-induced transport. From the very small to the very large scales

The study of fluctuation-induced transport is concerned with the directed motion of particles on a substrate when subjected to a fluctuating external field. Work over the last two decades provides now precise clues on how the average transport depends on three fundamental aspects: the shape of the substrate, the correlations of the fluctuations and the mass, geometry, interaction and density of the particles. These three aspects, reviewed here, acquire additional relevance because the same notions apply to a bewildering variety of problems at very different scales, from the small nano or micro-scale, where thermal fluctuations effects dominate, up to very large scales including ubiquitous cooperative phenomena in granular materials.

nlin.CD↗

arXiv2016

Quantum statistics of classical particles derived from the condition of free diffusion coefficient

We derive an equation for the current of particles in energy space; particles are subject to a mean field effective potential that may represent quantum effects. From the assumption that non-interacting particles imply a free diffusion coefficient in energy space we derive Maxwell-Boltzmann, Fermi-Dirac and Bose-Einstein statistics. Other new statistics are associated to a free diffusion coefficient; their thermodynamic properties are analyzed using the grand partition function. A negative relation between pressure and energy density for low temperatures can be derived, suggesting a possible connection with cosmological dark energy models.

cond-mat.stat-mech↗

arXiv2016

Current of interacting particles inside a channel of exponential cavities: Application of a modified Fick--Jacobs equation

The Fick--Jacobs equation has been widely studied, because of its applications in the diffusion and transport of non-interacting particles in narrow channels. It is also known that a modified version of this equation can be used to describe the same system with particles interacting through a hard-core potential. In this work we present a system that can be exactly solved using the Fick--Jacobs equation. The exact results of the particle concentration profile along the channel $n$, the current, $J$, and the mobility, $μ$, of particles as a function of an external force are contrasted with Monte Carlo simulations results of non-interacting particles. For interacting particles the behavior of $n$, $J$ and $μ$, obtained from the modified Fick--Jacobs equation are in agreement with numerical simulations, where the hard-core interaction is taken into account. Even more, for interacting particles the modified Fick--Jacobs equation gives comparatively more accurate results of the current difference (when a force is applied in opposite directions) than the exact result for the non-interacting ones.

cond-mat.stat-mech↗

arXiv2015

Transport with hard-core interaction in a chain of asymmetric cavities

In this paper we investigate the diffusion of particles inside a chain of asymmetric cavities. We are considering particles that interact through a hard--core potential and are driven by an external force. We show that the difference in the current when the force is applied to the left and to the right strongly depends on the concentration inside the cavity. We found that, when the concentration is high enough, the hard--core interaction vanishes and inverts the asymmetric effect of the cavity. We also introduce a new equation, a modification to the Fick--Jacobs equation, to describe this system analytically. Finally, we used numerical simulations to verify the analytic results, finding a good agreement between theory and simulations.

cond-mat.stat-mech↗