Luis Daniel Porfirio, García-González Alcione, Saint-Martin Humberto
CONACYT Research Fellow-Centro de Ingeniería y Desarrollo Industrial, Queréraro, Qro 76125, México.
Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León, Nuevo León 66451, México.
Int J Mol Sci. 2016 May 26;17(6):378. doi: 10.3390/ijms17060378.
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.
采用三种最新的水模型TIP4P/2005（可转移分子间四点势/2005）、TIP4P/Ice（可转移分子间四点势/冰）和TIP4Q（可转移分子间四电荷势），结合甲烷的两种模型：全原子模型OPLS-AA（液态最优参数化）和联合原子模型（UA），进行了蒙特卡罗模拟和分子动力学模拟；对后者应用了C-O相互作用校正，并用于第三组模拟。通过与1巴压力下280、300、330和370K时水合自由能的实验值以及145巴压力下277、283和291K时的实验径向分布函数进行比较，对模型进行了验证。无论用于σC,O的组合规则如何，均发现吻合良好，但应用UA模型校正时除外。因此，使用联合原子模型对sI水合物进行了进一步模拟，以将热膨胀系数与实验进行比较。使用UA甲烷模型和三种水模型进行了最后一组模拟，以研究80、230和400巴下sI水合物-液态水-气体的共存情况。将熔化温度与实验值进行了比较。结果表明，需要使用各种不同模型进行模拟，以获得所关注系统可靠且稳健的分子图像。
