Fourth-order Binder Cumulants Research Articles

Critical behavior in a chiral molecular model.

Understanding the condensed-phase behavior of chiral molecules is important in biology as well as in a range of technological applications, such as the manufacture of pharmaceuticals. Here, we use molecular dynamics simulations to study a chiral four-site molecular model that exhibits a second-order symmetry-breaking phase transition from a supercritical racemic liquid into subcritical D-rich and L-rich liquids. We determine the infinite-size critical temperature using the fourth-order Binder cumulant, and we show that the finite-size scaling behavior of the order parameter is compatible with the 3D Ising universality class. We also study the spontaneous D-rich to L-rich transition at a slightly subcritical temperature of T = 0.985Tc, and our findings indicate that the free energy barrier for this transformation increases with system size as N2/3, where N is the number of molecules, consistent with a surface-dominated phenomenon. The critical behavior observed herein suggests a mechanism for chirality selection in which a liquid of chiral molecules spontaneously forms a phase enriched in one of the two enantiomers as the temperature is lowered below the critical point. Furthermore, the increasing free energy barrier with system size indicates that fluctuations between the L-rich and D-rich phases are suppressed as the size of the system increases, trapping it in one of the two enantiomerically enriched phases. Such a process could provide the basis for an alternative explanation for the origin of biological homochirality. We also conjecture the possibility of observing nucleation at subcritical temperatures under the action of a suitable chiral external field.

New order parameter for the Higgs transition in SU(2) -Higgs theory

We investigate the Higgs transition within the four-dimensional $SU(2)$-Higgs model in search for an order parameter as a function of the Higgs field hopping parameter, $\ensuremath{\kappa}$, using lattice technique. We measure the Higgs condensate after applying Landau gauge fixing and study the corresponding susceptibility, magnetization, and fourth order Binder cumulant using four different spatial volumes with ${N}_{\ensuremath{\tau}}=2$. The computation is carried out with gauge coupling, ${\ensuremath{\beta}}_{g}=8$, for a range of scalar self-coupling, $\ensuremath{\lambda}={0.00010,0.00350}$, with an emphasis near the critical end point. Finite size scaling analysis of the gauge fixed condensate and its cumulants agree with the standard 3D Ising values $\ensuremath{\nu}=0.62997$, $\ensuremath{\beta}/\ensuremath{\nu}=0.518$, $\ensuremath{\gamma}/\ensuremath{\nu}=1.964$ at $\ensuremath{\lambda}=0.00150$. These results are in agreement with previous studies suggesting 3D Ising universality class. The numerical results also indicate that, at the transition point, the gauge fixed condensate vanishes in the infinite volume limit.

Фазовые переходы в двумерной слабо разбавленной четырехкомпонентной модели Поттса на гексагональной решетке

The Monte Carlo method is used to study phase transitions in a two-dimensional weakly diluted 4-state Potts model on a hexagonal lattice. Systems with linear dimensions L=21÷336 at spin concentrations p=1.00, 0.90 are considered. The use of the fourth-order binder cumulants method and histogram data analysis showed that the introduction of non-magnetic impurities has a stabilizing role in the implementation of the second-order phase transition in the Potts model under study on a hexagonal lattice.

Phase transitions in a two-dimensional weakly diluted 4-state Potts model on a hexagonal lattice

The Monte Carlo method is used to study phase transitions in a two-dimensional weakly diluted 4-state Potts model on a hexagonal lattice. Systems with linear dimensions L=21/336 at spin concentrations p=1.00, 0.90 are considered. The use of the fourth-order binder cumulants method and histogram data analysis showed that the introduction of nonmagnetic impurities has a stabilizing role in the implementation of the second-order phase transition in the Potts model under study on a hexagonal lattice. Keywords: Potts model, Monte Carlo method, thermodynamic parameters, disorder.

Ising model on a 2D additive small-world network

In this article, we have employed Monte Carlo simulations to study the Ising model on a two-dimensional additive small-world network (A-SWN). The system model consists of a LxL square lattice where each site of the lattice is occupied for a spin variable that interacts with the nearest neighbor and has a certain probability p of being additionally connected at random to one of its farther neighbors. The system is in contact with a heat bath at a given temperature T and it is simulated by one-spin flip according to the Metropolis prescription. We have calculated the thermodynamic quantities of the system, such as, the magnetization per spin m, magnetic susceptibility chi, and the reduced fourth-order Binder cumulant U as a function of T for several values of lattice size L and additive probability p. We also have constructed the phase diagram for the equilibrium states of the model in the plane T versus p showing the existence of a continuous transition line between the ferromagnetic F and paramagnetic P phases. Using the finite-size scaling (FSS) theory, we have obtained the critical exponents for the system, where varying the parameter p, we have observed a change in the critical behavior from the regular square lattice Ising model to A-SWN.

ESpinS: A program for classical Monte-Carlo simulations of spin systems

We present ESpinS (Esfahan Spin Simulation) package to evaluate the thermodynamic properties of spin systems described by a spin model Hamiltonian. In addition to the Heisenberg exchange term, the spin Hamiltonian in ESpinS can contain interactions such as bi-quadratic, Dzyaloshinskii–Moriya, and single-ion anisotropy. By applying the classical Monte Carlo simulation, ESpinS simulates the behavior of spin systems with respect to temperature. ESpinS can calculate the specific heat, susceptibility, staggered magnetization, energy histogram, fourth-order Binder cumulants, and neutron scattering structure factor. Further, it can compute the user-defined magnetic order parameter, that is, the summation of the projection of spins on the user-defined directions and the physical quantities based on it. ESpinS works with both a local update algorithm and a parallel tempering algorithm. The latter is an appropriate option for considering frustrated and spin-glass magnetic systems. ESpinS is written in Fortran 90 and can be run in single or parallel mode. The package is freely available under the GPL license (https://github.com/nafiserb/ESpinS).

Phase Transitions and the Thermodynamic Properties of the Potts Model with the Spin State Number q = 4 at a Kagome Lattice

Phase transitions and the thermodynamic properties of the two-dimensional ferromagnetic Izing model with spin state number q = 4 on a kagome lattice are studied by the Monte Carlo method on the base of the Wang–Landau algorithm. The phase transition character is analyzed using the fourth-order Binder cumulant method and the histogram analysis of the data. It is found that this model undergoes a first-order phase transition.

Effect of quenched non-magnetic impurities on phase transitions in a two-dimensional Potts model

The Wolff cluster Monte Carlo algorithm is used to investigate the effect of frozen nonmagnetic canonically distributed impurities on the phase transitions in a two-dimensional Potts model with the spin state q = 5. Systems with linear dimensions L = 20–160 at spin concentrations p = 1.0 and 0.9 are considered. Using the fourth-order Binder cumulant method and the histogram analysis method it is shown that if a weak quenched disorder in the form of non-magnetic impurities (p = 0.9) is introduced in the system, the first-order phase transition changes to a second-order phase transition.

Influence of Quenched Non-Magnetic Impurities on Phase Transitions in Low-Dimensional Potts Models

The effect of quenched non-magnetic impurities on phase transitions in low-dimensional Potts model structures is investigated by the Monte Carlo method using a cluster algorithm. Systems with linear dimensions of L = 20–160 and spin concentrations of p = 1.0, 0.9 are considered. Using the fourth-order Binder cumulant method and the histogram-data analysis method, the introduction of weak quenched disorder (p = 0.9) in the form of non-magnetic impurities is shown to change the order of the phase transition from the first to the second.

Phase Transitions in Low-Dimensional Disordered Potts Models

The Monte Carlo method is used to study phase transitions in disordered two-dimensional Potts models in which disorder is realized as nonmagnetic impurities. The temperature dependences of the thermodynamic parameters have been calculated for specific heat C, susceptibility χ, and fourth-order Binder cumulants in the dependence on spin concentration p. The calculations have been performed for the system with periodic boundary conditions. The systems with linear sizes L × L = N, L = 20–160 are considered. The incorporation of nonmagnetic impurities to a spin system is shown to possibly lead to a change of the first-order phase transition to a second-order phase transition. The problem of the universality classes of the critical behavior of low-dimensional diluted systems is discussed.

Phase Transformations and Thermodynamic Properties of the Potts Model with q = 4 on a Hexagonal Lattice with Interactions of Next-Nearest Neighbors

The magnetic structures of the ground state, phase transitions, and the thermodynamic properties of a two-dimensional ferromagnetic Potts model with the number of spin states q = 4 on a hexagonal lattice are studied using the Wang–Landau algorithm of the Monte Carlo method, taking into account the interactions of the nearest and the next-nearest neighbors. It is shown that the inclusion of the antiferromagnetic interactions of the next-nearest neighbors leads to the appearance of frustration and disturbance of magnetic ordering. The phase transition characters are analyzed using the method of fourth-order Binder cumulants and the histogram method. It is found that a first-order phase transition takes place in this model.

Фазовые переходы в низкоразмерных неупорядоченных моделях Поттса

Abstract The Monte Carlo method is used to study phase transitions in disordered two-dimensional Potts models in which disorder is realized as nonmagnetic impurities. The temperature dependences of the thermodynamic parameters have been calculated for specific heat C , susceptibility χ, and fourth-order Binder cumulants in the dependence on spin concentration p . The calculations have been performed for the system with periodic boundary conditions. The systems with linear sizes L × L = N , L = 20–160 are considered. The incorporation of nonmagnetic impurities to a spin system is shown to possibly lead to a change of the first-order phase transition to a second-order phase transition. The problem of the universality classes of the critical behavior of low-dimensional diluted systems is discussed.

Фазовые переходы в двумерной слабо разбавленной пятивершинной модели Поттса

Computer simulation was used to study phase transitions in the two-dimensional weakly diluted Potts model on a square lattice at q=5. Systems with linear dimensions L×L=N, L=10-120 are considered. Based on fourth-order Binder cumulants, it was shown that the introduction of nonmagnetic impurities into the spin system described by the two-dimensional Potts model with q=5 leads to a change in the first-order phase transition to the second-order phase transition.

Phase transitions in the Ising model on a triangular lattice with different values of interlayer exchange interaction

The Monte Carlo method was used to study the phase transitions and thermodynamic properties of the three-dimensional antiferromagnetic Ising model on a layered triangular lattice at various values of interlayer exchange interaction. A number of investigations have been carried out for the ratios of the intralayer (J1) and interlayer (J2) exchange interactions within the range of r = J2/J1 = 0.01–1.0. The nature of the phase transitions was studied using the fourth-order Binder cumulant method and histogram data analysis. It has been shown that in the considered range r, the transition from a disordered phase to an ordered phase is a second-order phase transition.

Consensus formation in continuous opinion dynamics on quasiperiodic lattices

We studied the Biswas–Chatterjee–Sen (BCS) consensus formation model, also known as the Kinetic Continuous Opinion Dynamics (KCOD) model on quasiperiodic lattices by using Kinetic Monte Carlo simulations and Finite Size Scaling technique. Our results are consistent with a continuous phase transition, controlled by an external noise. We obtained the order parameter [Formula: see text], defined as the averaged opinion, the fourth-order Binder cumulant [Formula: see text] and susceptibility [Formula: see text] as functions of the noise parameter. We estimated the critical noises for Penrose and Ammann–Beenker lattices. We also considered seven-fold and nine-fold quasiperiodic lattices and estimated the respective critical noises as well. Irrespective of rotational and translational long-range order of the lattice, the system falls in the same universality class of the two-dimensional Ising model. Quasiperiodic order is irrelevant and it does not change any critical exponents for BCS model.

Phase transitions in the two-dimensional four-vertex Potts model with quenched nonmagnetic impurities

The thermodynamic properties and phase transitions in the two-dimensional weakly diluted Potts model with the number of spin states q=4 were studied by the Monte Carlo method. Systems with linear dimensions L×L = N, L=10–160 are considered. Using the fourth order Binder cumulant method, critical temperatures were calculated for spin systems with a spin concentration p=1.0 and 0.90. Critical indices are calculated on the basis of the theory of finite-size scaling. The universality of the critical behavior of two-dimensional disordered systems is discussed.

Influence of quenched non-magnetic impurities on phase transitions in the two-dimensional Potts model with q = 5

Abstract Thermodynamic properties and phase transitions in 2d weakly diluted Potts model on a square lattice are investigated by the Monte Carlo method. We consider the systems with linear sizes L × L = N, L = 10–160. Using the fourth order Binder cumulant method, it was shown that the introduction of non-magnetic impurities into the spin system described by the two-dimensional Potts model with q = 5 leads to a change in the first-order phase transition to the second-order phase transition.

Critical Temperature of the Three-Vertex Potts Model on a Kagome Lattice

The Potts model on a Kagome lattice is considered. The Monte Carlo method is used to obtain the temperature dependences of the thermodynamic parameters: heat capacity C, order parameter m, and susceptibility χ. The calculations were performed for systems with periodic boundary conditions. Systems with linear dimensions L × L = N, L = 20–90, were considered. Based on the fourth-order Binder cumulant method, the critical temperature (Tc) was calculated for the three-vertex Potts model on a Kagome lattice. It is shown that the obtained value of Tc, within the statistical error, is in good agreement with the results obtained by the transfer matrix and polynomial approximation methods.

Фазовые переходы и термодинамические свойства модели Поттса с числом состояний спина q=4 на треугольной решетке

The Wang-Landau Monte Carlo algorithm has been used to study the phase transitions and thermodynamic properties of the two-dimensional ferromagnetic q = 4 Potts model on a triangular lattice. A nature of phase transition has estimated using the methods of the fourth order Binder cumulants and the histogram analysis. It has been established that a first-order phase transition is observed in the model under study.

Критическая температура трехвершинной модели Поттса на решетке Кагоме

The Potts model on the Kagome lattice is considered. The Monte Carlo method is used to obtain the temperature dependences of the thermodynamic parameters of heat capacity C, order parameter m, and susceptibility χ. The calculations were performed for systems with periodic boundary conditions. Systems with linear dimensions LxL = N, L = 20-90 were considered. Based on the fourth order Binder cumulant method, the critical temperature (Tc) was calculated for the three-vertex Potts model on the Kagome lattice. It is shown that the obtained Tc value within the statistical error is in good agreement with the results obtained using the transfer-matrix and polynomial approximation methods.