title: A Theoretical Study of the Hydration of Methane, from the Aqueous Solution to the sI Hydrate-Liquid Water-Gas Coexistence.
abstract: Monte Carlo and molecular dynamics simulations were done with three recent water models TIP4P/2005 (Transferable Intermolecular Potential with 4 Points/2005), TIP4P/Ice (Transferable Intermolecular Potential with 4 Points/ Ice) and TIP4Q (Transferable Intermolecular Potential with 4 charges) combined with two models for methane: an all-atom one OPLS-AA (Optimal Parametrization for the Liquid State) and a united-atom one (UA); a correction for the C-O interaction was applied to the latter and used in a third set of simulations. The models were validated by comparison to experimental values of the free energy of hydration at 280, 300, 330 and 370 K, all under a pressure of 1 bar, and to the experimental radial distribution functions at 277, 283 and 291 K, under a pressure of 145 bar. Regardless of the combination rules used for σC,O, good agreement was found, except when the correction to the UA model was applied. Thus, further simulations of the sI hydrate were performed with the united-atom model to compare the thermal expansivity to the experiment. A final set of simulations was done with the UA methane model and the three water models, to study the sI hydrate-liquid water-gas coexistence at 80, 230 and 400 bar. The melting temperatures were compared to the experimental values. The results show the need to perform simulations with various different models to attain a reliable and robust molecular image of the systems of interest.
authors.affiliation: CONACYT Research Fellow-Centro de Ingenier&#237;a y Desarrollo Industrial, Quer&#233;raro, Qro 76125, M&#233;xico. dpluisji@conacyt.mx.
authors.forename: Daniel Porfirio
authors.initials: DP
authors.lastname: Luis
authors.affiliation: Facultad de Ciencias Qu&#237;micas, Universidad Aut&#243;noma de Nuevo Le&#243;n, Nuevo Le&#243;n 66451, M&#233;xico. alcione.garciagn@uanl.edu.mx.
authors.forename: Alcione
authors.initials: A
authors.lastname: García-González
authors.affiliation: Instituto de ciencias F&#237;sicas, Universidad Nacional Aut&#243;noma de M&#233;xico, Apartado Postal 48-3, Cuernavaca, Morelos 62251, M&#233;xico. hstmartin@fis.unam.mx.
authors.forename: Humberto
authors.initials: H
authors.lastname: Saint-Martin
mesh_terms: D008697:Methane / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D009010:Monte Carlo Method; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D008697:Methane
keywords: analytical model potentials; hydrates; numerical simulations; phase coexistence