arXiv subjects

Francisco Sastre

Publications and source records attributed to Francisco Sastre.

10 recordsLinked to original sources

arXiv2024

Numerical simulations for the Ising model on three dimensional lattices with coordination number equal 5: static and dynamic critical phenomena

In this work we performed numerical simulations for the Ising model on three dimensional lattices with coordination number equal 5. With Monte Carlo simulations in the static case we evaluated the critical temperature and the static critical exponents $ν$, $γ$ and $β$. Once that we have the critical temperature value we investigated the dynamical critical behavior with Glauber dynamics, starting from disordered states. From our simulations we obtained the values for the dynamic exponent $z=2.037(8)$, the exponent for the autocorrelation $λ/z=1.364(5)$, the exponent of the critical initial increase $θ'=0.109(8)$ and the asymptotic value of the fluctuation-dissipation ratio $X^\infty=0.433(1)$. All of these results are in good agreement to the previous values reported for the 3D Ising model universality class.

cond-mat.stat-mech↗

arXiv2021

Critical point determination from probability distribution functions in the three dimensional Ising model

In this work we propose a new numerical method to evaluate the critical point, the susceptibility critical exponent and the correlation length critical exponent of the three dimensional Ising model without external field using an algorithm that evaluates directly the derivative of the logarithm of the probability distribution function with respect to the magnetisation. Using standard finite-size scaling theory we found that correction-to-scaling effects are not present within this approach. Our results are in good agreement with previous reported values for the three dimensional Ising model.

cond-mat.stat-mech↗

arXiv2019

Critical temperature determination on a square-well fluid using an adaptation of the Microcanonical-ensemble computer simulation method

In this work a novel method to evaluate the liquid-vapor critical temperature using a generalization of the Microcanonical-ensemble computer simulation method (MCE) is presented. The isotherms of the chemical potential versus densities are obtained for a square-well (SW) fluid with interaction range $λ/σ= 1.5$: From these curves it can be extracted the critical temperature for different system sizes observing the change of the slope from the chemical potential's curve in the critical region as function of the temperature. Working with different systems sizes and Finite Size Scaling (FSS) Theory the critical temperature $T_c=1.2180(29)$ and the critical exponent $ν=0.65(3)$ are obtained, without previous knowledge of $T_c$ or $ν$. These results are in good agreement with the reported values for this system.

cond-mat.stat-mech↗

arXiv2017

Microcanonical-ensemble computer simulation of the high-temperature expansion coefficients of the Helmholtz free-energy of a Square-well fluid

The Microcanonical Ensemble computer simulation method (MCE) is used to evaluate the perturbation terms $A_i$ of the Helmholtz free energy of a Square-Well (SW) fluid. The MCE method offers a very efficient and accurate procedure for the determination of perturbation terms of discrete-potential systems such as the SW fluid and surpass the standard NVT Canonical Ensemble Monte Carlo method, allowing the calculation of the first six expansion terms. Results are presented for the case of a SW potential with attractive ranges $1.1 \le λ\le 1.8$. Using semiempirical representation of the MCE values for $A_i$, we also discuss the accuracy in the determination of the phase diagram of this system.

cond-mat.stat-mech↗

arXiv2015

An alternative order-parameter for non-equilibrium generalized spin models on honeycomb lattices

An alternative definition for the order-parameter is proposed, for a family of non-equilibrium spin models with up-down symmetry on honeycomb lattices, and which depends on two parameters. In contrast to the usual definition, our proposal takes into account that each site of the lattice can be associated with a local temperature which depends on the local environment of each site. Using the generalised voter motel as a test case, we analyse the phase diagram and the critical exponents in the stationary state and compare the results of the standard order-parameter with the ones following from our new proposal, on the honeycomb lattice. The stationary phase transition is in the Ising universality class. Finite-size corrections are also studied and the Wegner exponent is estimated as $ω=1.06(9)$.

cond-mat.stat-mech↗

arXiv2015

Antiferromagnetic majority voter model on square and honeycomb lattices

An antiferromagnetic version of the well-known majority voter model on square and honeycomb lattices is proposed. Monte Carlo simulations give evidence for a continuous order-disorder phase transition in the stationary state in both cases. Precise estimates of the critical point are found from the combination of three cumulants, and our results are in good agreement with the reported values of the equivalent ferromagnetic systems. The critical exponents $1/ν$, $γ/ν$ and $β/ν$ were found. Their values indicate that the stationary state of the antiferromagnetic majority voter model belongs to the Ising model universality class.

cond-mat.stat-mech↗

arXiv2015

Microcanonical ensemble simulation method applied to discrete potential fluids

In this work we extend the applicability of the microcanonical ensemble simulation method, originally proposed to study the Ising model (A. Hüller and M. Pleimling, Int. Journal of Modern Physics C, 13, 947 (2002), arxiv:cond-mat/0110090), to the case of simple fluids. An algorithm is developed by measuring the transition rates probabilities between macroscopic states, that has as advantage with respect to conventional Monte Carlo NVT (MC-NVT) simulations that a continuous range of temperatures are covered in a single run. For a given density, this new algorithm provides the inverse temperature, that can be parametrized as a function of the internal energy, and the isochoric heat capacity is then evaluated through a numerical derivative. As an illustrative example we consider a fluid composed of particles interacting via a square-well (SW) pair potential of variable range. Equilibrium internal energies and isochoric heat capacities are obtained with very high accuracy compared with data obtained from MC-NVT simulations. These results are important in the context of the application of Hüller-Pleimling method to discrete-potential systems, that are based on a generalization of the SW and Square-Shoulder fluids properties.

cond-mat.stat-mech↗

arXiv2012

Critical phenomena of the Majority voter model in a three dimensional cubic lattice

In this work we investigate the critical behavior of the three dimensional simple-cubic Majority voter model. Using numerical simulations and a combination of two different cumulants we evaluated the critical point with a higher accuracy than the previous numerical result found by Yang et al. [J.- S. Yang, I.-M. Kim and W. Kwak, Phys. Rev. E 77, 051122 (2008)]. Using standard Finite Size Scaling theory and scaling corrections we find that the critical exponents ν, γ and β are the same as those of the three dimensional Ising model.

cond-mat.stat-mech↗

arXiv2009

Short-time dynamic in the Majority vote model: The ordered and disordered initial cases

This work presents short-time Monte Carlo simulations for the two dimensional Majority-vote model starting from ordered and disordered states. It has been found that there are two pseudo-critical points, each one within the error-bar range of previous reported values performed using fourth order cumulant crossing method. The results show that the short-time dynamic for this model has a dependence on the initial conditions. Based on this dependence a method is proposed for the evaluation of the pseudo critical points and the extraction of the dynamical critical exponent $z$ and the static critical exponent $β/ν$ for this model.

cond-mat.stat-mech↗

arXiv2003

Bona Fide Thermodynamic Temperature in Nonequilibrium Kinetic Ising Models

We show that a nominal temperature can be consistently and uniquely defined everywhere in the phase diagram of large classes of nonequilibrium kinetic Ising spin models. In addition, we confirm the recent proposal that, at critical points, the large-time ``fluctuation-dissipation ratio'' $X_\infty$ is a universal amplitude ratio and find in particular $X_\infty \approx 0.33(2)$ and $X_\infty = 1/2$ for the magnetization in, respectively, the two-dimensional Ising and voter universality classes.

cond-mat.stat-mech↗