Configurational-bias Monte Carlo Gibbs ensemble

B. Configurational-Bias Monte Carlo in the Gibbs Ensemble... 

To improve the sampling of insertions of flexible molecules, such as the alkanes, the configurational-bias Monte Carlo technique [29,32-35,37,59] can be used. Configurational-bias Monte Carlo replaces the conventional random insertion of entire molecules with a scheme in which the chain molecule is inserted atom by atom such that conformations with favorable energies are preferentially found. The resulting bias of the particle-swap step in the Gibbs ensemble is removed by special acceptance rules [60,61] [compare to Eq. (3.3) of first chapter in this volume]... 

Configurational-bias Monte Carlo in the Gibbs ensemble has been successfully applied to the calculations of single-component vapor-liquid phase equilibria of linear and branched alkanes [61,63-67], alcohols [68,69], and a fatty-acid Langmuir monolayer [70]. The extension to multicomponent mixtures introduces a case in which the smaller molecules (members of a homologous series) have a considerably higher acceptance rate in the swap move than do larger molecules. In recent simulations for alkane mixtures... 

Panagiotopoulos and coworkers [51] use the same parameters as Larson for the study of phase behavior, but with two different simulation methodologies. The first technique is the Gibbs ensemble method, in which each bulk phase is simulated in a separate cell and molecules are interchanged and volumes adjusted between the two for equilibration of the system [52]. The second is a standard canonical ensemble simulation, like Larson s, but employs the configurational bias Monte Carlo method. The configurational bias Monte Carlo method is much more efficient than the ones based on reptation and other local moves but is not useful if any dynamic information is sought from the simulations. 

Abstract The use of configurational-bias Monte Carlo simulations in tbe Gibbs ensemble allows for the sampling of phenomena that occur on vastly different time and length scales. In this review, applications of this simulation approach to probe retention in gas and reversed-phase liquid chromatographic systems are discussed. These simulations provide an unprecedented view of the retention processes at the molecular-level and show excellent agreement with experimental retention data. 

Abstract Configurational-bias Monte Carlo simulations in the Gibbs ensemble have been carried out to determine the vapor-liquid coexistence curve for a pentadecanoic acid Langmuir monolayer. Two different force fields were studied (i) the original monolayer model of Karaborni and Toxvaerd including anisotropic interactions between alkyl tails, and (ii) a modified version of this model which uses an isotropic united-atom description for the methylene and methyl groups and includes dispersive interactions between the tail segments and the water surface. 

The combination of Gibbs-ensemble and configurational-bias Monte Carlo is a viable technique to calculate the fluid phase diagrams of monolayer systems (in addition to bulk systems for which the technique has been previously used). However, for the relatively complex fatty acid Lang-... 

Siepmann et al. have used the combination of the Gibbs-ensemble technique and configurational-bias Monte-Carlo to simulate vapor-liquid equilibria of the n-alkanes at conditions where experiments are not (yet) feasible. Phase diagrams are very sensitive to the choice of interaction potentials. Most available models for alkanes have been obtained by fitting simulation data to experimental properties of the liquid under standard conditions. In Figure 6 the vapor- liquid curve of octane as predicted by some of these models is compared with experimental data. This figures shows that the models... 

S. T. Cui, P. T. Cummings, and H. D. Cochran, Fluid Phase Equilibria, 141, 45 (1997). Configurational Bias Gibbs Ensemble Monte Carlo Simulation of Vapor-Liquid Equilibria of Linear and Short-Branched Alkanes. 

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