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Comparing the use of gibbs ensemble and grand-canonical transition-matrix Monte Carlo methods to determine phase equilibria / Andrew S. Paluch in Industrial & engineering chemistry research, Vol. 47 N° 13 (Juillet 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N° 13 (Juillet 2008) . - p. 4533–4541 Titre : Comparing the use of gibbs ensemble and grand-canonical transition-matrix Monte Carlo methods to determine phase equilibria Type de document : texte imprimé Auteurs : Andrew S. Paluch, Auteur ; Vincent K. Shen, Auteur ; Jeffrey R. Errington, Auteur Année de publication : 2008 Article en page(s) : p. 4533–4541 Note générale : Bibliogr. p. 4541 Langues : Anglais (eng) Mots-clés : Gibbs  ensemble;  GC-TMMC  methods;  Molecular  fluids Résumé : We present results from a computational study investigating the use of Gibbs ensemble and grand-canonical transition-matrix Monte Carlo (GC-TMMC) methods to determine the liquid−vapor phase coexistence properties of pure molecular fluids of varying degrees of complexity. The molecules used in this study were ethane, n-octane, cyclohexane, 2,5-dimethylhexane, 1-propanol, and water. We first show that the GC-TMMC method can reproduce Gibbs ensemble results found in the literature. Given the excellent agreement for each molecule, we then compare directly the performance of Gibbs ensemble and GC-TMMC simulations at both low and high reduced temperatures by monitoring the relative uncertainties in the saturation properties as a function of computational time. In general, we found that the GC-TMMC method yielded limiting uncertainties in the saturated vapor density and pressure that were significantly smaller, by an order of magnitude in some instances, than those of the Gibbs ensemble method. Limiting Gibbs ensemble uncertainties for these properties were generally in the 0.8−5.0% range. However, both methods yielded comparable limiting uncertainties in the saturated liquid density, which fell within the range of 0.1−1.0%. In the case of water at 300 K, we found that the Gibbs ensemble outperformed GC-TMMC. The relatively poor performance of the GC-TMMC method in this situation was tied to the slow convergence of the density probability distribution at this low temperature. We also discuss strategies for improving the convergence rate under these conditions. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800143n [article] Comparing the use of gibbs ensemble and grand-canonical transition-matrix Monte Carlo methods to determine phase equilibria [texte imprimé] / Andrew S. Paluch, Auteur ; Vincent K. Shen, Auteur ; Jeffrey R. Errington, Auteur . - 2008 . - p. 4533–4541. Bibliogr. p. 4541 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N° 13 (Juillet 2008) . - p. 4533–4541 Mots-clés : Gibbs  ensemble;  GC-TMMC  methods;  Molecular  fluids Résumé : We present results from a computational study investigating the use of Gibbs ensemble and grand-canonical transition-matrix Monte Carlo (GC-TMMC) methods to determine the liquid−vapor phase coexistence properties of pure molecular fluids of varying degrees of complexity. The molecules used in this study were ethane, n-octane, cyclohexane, 2,5-dimethylhexane, 1-propanol, and water. We first show that the GC-TMMC method can reproduce Gibbs ensemble results found in the literature. Given the excellent agreement for each molecule, we then compare directly the performance of Gibbs ensemble and GC-TMMC simulations at both low and high reduced temperatures by monitoring the relative uncertainties in the saturation properties as a function of computational time. In general, we found that the GC-TMMC method yielded limiting uncertainties in the saturated vapor density and pressure that were significantly smaller, by an order of magnitude in some instances, than those of the Gibbs ensemble method. Limiting Gibbs ensemble uncertainties for these properties were generally in the 0.8−5.0% range. However, both methods yielded comparable limiting uncertainties in the saturated liquid density, which fell within the range of 0.1−1.0%. In the case of water at 300 K, we found that the Gibbs ensemble outperformed GC-TMMC. The relatively poor performance of the GC-TMMC method in this situation was tied to the slow convergence of the density probability distribution at this low temperature. We also discuss strategies for improving the convergence rate under these conditions. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800143n

Structure, stability, and upture of free and supported liquid films and assemblies in molecular simulations / Rahul Godawat in Industrial & engineering chemistry research, Vol. 47 N°10 (Mai 2008)

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N°10 (Mai 2008) . - p. 3582–3590 Titre : Structure, stability, and upture of free and supported liquid films and assemblies in molecular simulations Type de document : texte imprimé Auteurs : Rahul Godawat, Auteur ; Sumanth N. Jamadagni, Auteur ; Jeffrey R. Errington, Auteur Année de publication : 2008 Article en page(s) : p. 3582–3590 Note générale : Bibliogr. 3589-3590 Langues : Anglais (eng) Mots-clés : Films  --  Structure  --  Stability Résumé : Attractive interactions between molecules lead to formation of the liquid phase at sufficiently low temperatures. In the absence of external fields or containers, liquids assume the shape of spherical drops, which minimize their surface area. In systems with 3-D periodic boundary conditions (PBCs), which are routinely employed in molecular simulations, alternate configurations can be stable depending on the extent of the system. The stability of a variety of structures under 3-D PBCs originates from the underlying variation of free energy with density as shown elegantly by MacDowell and co-workers (MacDowell, L. G.; Shen, V. K.; Errington, J. R. J. Chem. Phys. 2006, 125, 3.). Here we present analysis of extensive Monte Carlo and molecular dynamics simulations of Lennard-Jones and water fluids to calculate free energy and explore the phase diagram that governs formation of different liquid assemblies. We also study metastability of different shapes and their interconversions by systematically initializing simulations in various configurations. Further, We present results on the rupture of thin liquid films on solid substrates, with focus on the evolution of liquid structure and the rupture mechanism. Our estimates of important capillary wavelengths from simulations are in good agreement with theoretical predictions of Vrij and Overbeek (Vrij, A.; Overbeek, J. T. J. Am. Chem. Soc. 1968, 90, 3074−3078.). Collectively, our work significantly extends the previous simulation studies of interfacial systems, and especially of thin-film structure, stability, and rupture processes in molecular simulations. [article] Structure, stability, and upture of free and supported liquid films and assemblies in molecular simulations [texte imprimé] / Rahul Godawat, Auteur ; Sumanth N. Jamadagni, Auteur ; Jeffrey R. Errington, Auteur . - 2008 . - p. 3582–3590. Bibliogr. 3589-3590 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N°10 (Mai 2008) . - p. 3582–3590 Mots-clés : Films  --  Structure  --  Stability Résumé : Attractive interactions between molecules lead to formation of the liquid phase at sufficiently low temperatures. In the absence of external fields or containers, liquids assume the shape of spherical drops, which minimize their surface area. In systems with 3-D periodic boundary conditions (PBCs), which are routinely employed in molecular simulations, alternate configurations can be stable depending on the extent of the system. The stability of a variety of structures under 3-D PBCs originates from the underlying variation of free energy with density as shown elegantly by MacDowell and co-workers (MacDowell, L. G.; Shen, V. K.; Errington, J. R. J. Chem. Phys. 2006, 125, 3.). Here we present analysis of extensive Monte Carlo and molecular dynamics simulations of Lennard-Jones and water fluids to calculate free energy and explore the phase diagram that governs formation of different liquid assemblies. We also study metastability of different shapes and their interconversions by systematically initializing simulations in various configurations. Further, We present results on the rupture of thin liquid films on solid substrates, with focus on the evolution of liquid structure and the rupture mechanism. Our estimates of important capillary wavelengths from simulations are in good agreement with theoretical predictions of Vrij and Overbeek (Vrij, A.; Overbeek, J. T. J. Am. Chem. Soc. 1968, 90, 3074−3078.). Collectively, our work significantly extends the previous simulation studies of interfacial systems, and especially of thin-film structure, stability, and rupture processes in molecular simulations.