Gibbs Ensemble Monte Carlo Method Research Articles

Application of a new Gibbs ensemble Monte Carlo method to site-site interaction model fluids

A new Gibbs ensemble Monte Carlo simulation method has been tested for rigid site–site interaction model fluids. In this method the total system is considered at constant enthalpy, pressure and number of particles. Vapour-liquid equilibrium data were determined for a potential model of liquid carbon disulphide and a potential model of liquid hydrogen sulphide. Conventional Gibbs ensemble Monte Carlo simulations were also carried out for comparison. The two methods yielded essentially the same results, but the new scheme showed some advantages.

Gibbs Ensemble Monte Carlo simulation of binary vapor-liquid equilibria for CFC alternatives

The Gibbs Ensemble Monte Carlo (GEMC) simulation method has been used for vapor-liquid equilibrium calculations of the binary systems R22-R142b and R22-R152a, which are considered to be promising mixture refrigerants for replacing R12. All the molecules have been treated in terms of an effective Lennard-Jones potential, with temperature dependent parameters regressed by fitting vapor pressures and saturated liquid densities at various temperatures for pure substances of interest. Good agreement between experimental and calculated data from the volume-translation Peng-Robinson equation of state and our simulated results, including the compositions, molar volumes for both the vapor and liquid phases, and heats of vaporization, indicates that the GEMC method can be applied to the description of phase behavior for these CFC alternative binary systems.

Properties of coexisting fluid phases of a binary system methanolethane by computer simulation

Methaneethane and methanolethane binary mixtures were simulated by the Gibbs ensemble Monte Carlo method. Thermodynamic properties and structural characteristics of coexisting fluid phases were calculated. Reasonable agreement with experiment was obtained, in particular, for the liquid-liquid-vapour coexisting pressure in the methanolethane system at 298.15 K. A lyophobic effect, which affects the phase behaviour and the hydrogen-bonding characteristics of the liquid phase, was observed. In order to improve agreement with experiment, the values of the Lennard-Jones interactions parameters for CH 3OH and C 2H 6 molecules were adjusted.

Fluid phase equilibria using molecular dynamics: the surface tension of chlorine and hexane

In this paper we demonstrate that the direct molecular dynamics method can be used to predict accurate fluid phase equilibria for molecular fluids. The method is applied to chlorine and n-hexane to calculate the coexisting densities, vapour pressure, and surface tension as a function of temperature. Chlorine is modelled as a rigid diatomic molecule, and n-hexane as an isotropic united-atom model. For hexane we use two sets of parameters for the intermolecular potential. The main difference in the parameters is the strength of the repulsion-dispersion interaction of the terminal methyl group eCH3 /k = 90·44 K (model I) and = 114 K (model II); systematic differences in the calculated properties are found for the models. For chlorine, the liquid-vapour densities and vapour pressures are in excellent agreement with experimental results, and with those previously calculated using the Gibbs ensemble Monte Carlo method (GEMC). Good agreement with the experimental surface tensions is obtained. For hexane, the cal...

Molecular simulations of enthalpies for CH 4C 2H 6CO 2 mixtures at saturation conditions

Enthalpies for methane-ethane-carbon dioxide mixtures at low temperature and high pressure saturation conditions were calculated by the Gibbs ensemble Monte Carlo method. The Lennard-Jones potential function was employed to describe the site-site intermolecular interactions. Molecules of both methane and carbon dioxide were treated as spherical while those of ethane were treated as linear with two methyl groups. The total number of molecules adopted in all simulations was 300. A comparison of the simulated data with the results obtained from the Peng-Robinson equation of state yields a reasonable agreement.

Molecular simulation of liquid-liquid equilibria for Lennard-Jones fluids

Abstract Guo M.X., Li Y.G., Li Z.C. and Lu J.F., 1994. Molecular simulation of liquid-liquid equilibria for Lennard-Jones fluids. Fluid Phase Equilibria , 98: 129-139. In this work, the liquid-liquid phase behavior of Lennard-Jones fluids was simulated by a Gibbs ensemble Monte Carlo (GEMC) method. To improve the convergence of simulation on such high-density systems, an “Internal Identity Interchange” move was proposed and added to the original GEMC method. Five binary mixtures were designed to examine the effects of various molecular parameters on the immiscibility of the two coexistence liquid phases. To study the influences of the two cross-molecular parameters (ϵ 12 and σ 12 ) on the immiscibility of the coexistence liquid phases, the Lorentz-Berthelot combining rules were linearly scaled through multiplication by two constants.

Molecular simulation of phase equilibria: simple, ionic and polymeric fluids

Recent advances in molecular simulation methodologies have enabled the calculation of phase equilibria for model fluids with unprecedented speed and accuracy. In this paper, we first briefly review the Gibbs ensemble Monte Carlo method for direct determination of phase coexistence. A new application of the Gibbs ensemble technique to the restricted primitive model of ionic systems is described in detail. The calculated phase coexistence envelope is in disagreement with most previous theoretical and numerical estimates. Our result for the reduced critical temperature is T c ∗ = 0.056 and for the reduced critical density ϱ c ∗ = 0.04. A recently developed technique for the calculation of the chemical potentials of polymeric fluids is also discussed and a tentative phase diagram for a homopolymer of length n = 20 segments is presented. We conclude with a discussion of potential future applications of molecular simulation techniques to the prediction of equilibrium properties of fluids.

Direct Determination of Fluid Phase Equilibria by Simulation in the Gibbs Ensemble: A Review

Abstract This paper provides an extensive review of the literature on the Gibbs ensemble Monte Carlo method for direct determination of phase coexistence in fluids. The Gibbs ensemble technique is based on performing a simulation in two distinct regions in a way that ensures that the conditions of phase coexistence are satisfied in a statistical sense. Contrary to most other available techniques for this purpose, such as thermodynamic integration, grand canonical Monte Carlo or Widom test particle insertions, the Gibbs ensemble technique involves only a single simulation per coexistence point. A significant body of literature now exists on the method, its theoretical foundations, and proposed modifications for efficient determination of equilibria involving dense fluids and complex intermolecular potentials. Some practical aspects of Gibbs ensemble simulation are also discussed in this review. Applications of the technique to date range from studies of simple model potentials (for example Lennard–Jones, square-well or Yukawa fluids) to calculations of equilibria in mixtures with components described by realistic potentials. We conclude by discussing the limitations of the technique and potential future applications.

Computer Simulation Study of Adsorption, Isosteric Heat and Phase Transitions of Methane on Graphite

AbstractWe report Canonical (NVTMC), Grand Canonical (GOMC) and Gibbs Ensemble Monte Carlo (GEMC) simulations for adsorption of methane on graphite. Lennard-Jones (LJ) potentials are used for the intermolecular interactions, and both structured and structureless (10–4–3) solid-fluid potentials are considered. Several sets of methane-methane L.I parameters have been used in the literature, and we compare results obtained with these sets throughout our simulations. The adsorption isotherm and isosteric heat curve are obtained at 77.5 K and found in good agreement with experiments. The commensurateincommensurate transition (CIT) of methane on a graphite substrate with periodically varying adsorbate-adsorbent potential at 40.0 K is studied and is in qualitative agreement with experiment. The effect of varying the corrugation of the fluid-wall potential on the commensurate and incommensurate phases is explored. The GEMC simulations have been carried out to study the vapor-liquid equilibrium (VLE) of a two-dimensional (2D) LJ fluid with system sizes up to 3000 particles. The effect of system sizes on the critical behavior is investigated. The GEMC method has also been successfully applied to study the VLE in 2D adsorbed films for the first time.