Configurational-bias Monte-Carlo simulations

Pablo J J, M Laso, JI Siepmann and U W Suter 1993. Continuum-Configurational Bias Monte Carlo Simulations of Long-chain Alkanes. Molecular Physics 80 55-63. 

Using configurational-bias Monte Carlo simulations we quantify how molecular sieves shape selectively modify the free energy of formation of adsorbed hydrocarbons. This allows for a basic thermodynamic analysis to explain the differences in alkane hydroconversion between MFI- and MEL-type molecular sieves, and regularities in the alkane yields of TON-type molecular sieves. 

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. 

Jiang J, Sandler SI, Schenk M, Smit B. Adsorption and separation of linear and branched alkanes on carbon nanombe bundles from configurational-bias Monte Carlo simulation. Phys... 

Vendruscolo, M. Modified configurational bias Monte Carlo method for simulation of polymer systems. J. Chem. Phys. 1997, 106, 2970-6. 

Escobedo, F.A., De Pablo, J.J. Extended continuum configurational bias Monte Carlo methods for simulation of flexible molecules. J. Chem. Phys. 1995, 102, 2636-52. 

The configuration-bias Monte Carlo (CB-MC) technique (112) has also been extensively applied to characterize the sorption of alkanes, principally in silicalite (111, 156, 168-171) but also in other zeolites (172-174). Smit and Siepmann (111, 168) presented a thorough study of the energetics, location, and conformations of alkanes from n-butane to n-dodecane in silicalite at room temperature. A loading of infinite dilution was simulated, based on a united-atom model of the alkanes and a zeolite simulation box of 16 unit cells. Potential parameters were very similar to those used in the MD study of June et al. (85). As expected, the static properties (heat of adsorption, Henry s law coefficient) determined from the CB-MC simulations are therefore in close agreement with the values of June et al. The... 

Pressure Swing Adsorption (PSA) unit is a dynamic separation process. In order to create a precise model of the process and thus an accurate design, it is necessary to have a good knowledge of the mixture s adsorption behaviour. Consequently, the dilAision rates in the adsorbent particles and the mixture isotherms are extremely vital data. This article intends to present a new approach to study the adsorption behaviour of isomer mixtures on zeolites. In a combined simulation and experimental project we set out to assess the sorption properties of a series of zeolites. The simulations are based on the configurational-bias Monte Carlo technique. The sorption data are measured in a volumetric set-up coupled with an online Near Infra-Red (NIR) spectroscopy, to monitor the bulk composition. Single component isotherms of butane and iso-butane were measured to validate the equipment, and transient volumetric up-take experiments were also performed to access the adsorption kinetics. 

Frenkel [3,7] has recently given a review of configurational bias methods for simulation of polymers. An account of these methods and their application to phase equilibria calculations is also described in the first chapter in this volume (by I. Siepmann). Here we merely outline the main ideas behind them (see also Fig. 1). In a configurational bias Monte Carlo move... 

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... 

Martin M G and J I Siepmann 1999. Novel Configurational-bias Monte Carlo Method tor Branched Molecules Transferable Potentials for Phase Equilibria. 2 United-atom Description of Branched Alkanes Journal of Physical Chemistry 103 4508-4517 Metropolis N, A W Rosenbluth, M N Rosenbluth, A H Teller and E Teller 1953 Equation of State Calculations by Fast Computing Machines. Journal of Chemical Physics 21 1087-1092 Okamoto Y and U H E Hansmann 1995. Thermodynamics of HeUx-coU Transitions Studied by Multicanomcal Algorithms. Journal of Physical Chemistry 99 11276-11287 Panagiotopoulos A Z 1987. Direct Determination of Phase Coexistence Properties of Fluids by Monte Carlo Simulation in a New Ensemble. Molecular Physics 61.813-826 Pangali C, M Rao and B J Berne 1978 On a Novel Monte Carlo Scheme for Simulating Water and Aqueous Solutions Chemical Physics Letters 55 413-417. 

The value of S(Q) at zero Q value cannot be determined experimentally on the same instrument that is used to measure diffusivities there are not enough points at small Q in Fig. 8b. However, the S(Q) scale, which is given in Fig. 8b in arbitrary units, can be renormalized. At infinite dilution, S(0) should be equal to one (hke in a gas), and sorption thermodynamics also imply that the thermodynamic correction factor should be equal to one, so that Eq. 38 will be fulfilled. On the other hand, at high concentrations, F increases while S(0) goes down. In Fig. 8b, r is equal to 6.6 for a concentration of 14 CF4 per u.c. so that S(0) should go down to 0.15. A more quantitative analysis has been recently performed for n-hexane and n-heptane in sihcalite [36] where the inverse of the thermodynamic factor, calculated from S(Q) was found to be in good agreement with configurational-bias Monte Carlo (CBMC) simulations. 

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. 

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