Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200, USA.
J Phys Chem B. 2013 Jul 3;117(26):8018-30. doi: 10.1021/jp404207x. Epub 2013 Jun 21.
We discuss Monte Carlo (MC) simulation methods for calculating liquid-vapor saturation properties of ionic liquids. We first describe how various simulation tools, including reservoir grand canonical MC, growth-expanded ensemble MC, distance-biasing, and aggregation-volume-biasing, are used to address challenges commonly encountered in simulating realistic models of ionic liquids. We then indicate how these techniques are combined with histogram-based schemes for determining saturation properties. Both direct methods, which enable one to locate saturation points at a given temperature, and temperature expanded ensemble methods, which provide a means to trace saturation lines to low temperature, are discussed. We study the liquid-vapor phase behavior of the restricted primitive model (RPM) and a realistic model for 1,3-dimethylimidazolium tetrafluoroborate ([C1mim][BF4]). Results are presented to show the dependence of saturation properties of the RPM and [C1mim][BF4] on the size of the simulation box and the boundary condition used for the Ewald summation. For [C1mim][BF4] we also demonstrate the ability of our strategy to sample ion clusters that form in the vapor phase. Finally, we provide the liquid-vapor saturation properties of these models over a wide range of temperature. Overall, we observe that the choice of system size and boundary condition have a non-negligible effect on the calculated properties, especially at high temperature. Also, we find that the combination of grand canonical MC simulation and isothermal-isobaric temperature expanded ensemble MC simulation provides a computationally efficient means to calculate liquid-vapor saturation properties of ionic liquids.
我们讨论了用于计算离子液体汽液饱和性质的蒙特卡罗（MC）模拟方法。我们首先描述了如何使用各种模拟工具，包括储库巨正则 MC、生长扩展系综 MC、距离偏差和聚集体积偏差，来解决模拟离子液体实际模型时常见的挑战。然后，我们指出了如何将这些技术与基于直方图的方案结合起来以确定饱和性质。我们讨论了既可以在给定温度下定位饱和点的直接方法，也可以追踪饱和线至低温的扩展温度系综方法。我们研究了受限原始模型（RPM）和 1,3-二甲基咪唑四氟硼酸盐([C1mim][BF4])的实际模型的汽液相行为。结果表明，RPM 和 [C1mim][BF4]的饱和性质取决于模拟盒的大小和用于 Ewald 求和的边界条件。对于 [C1mim][BF4]，我们还展示了我们的策略能够对在气相中形成的离子簇进行采样的能力。最后，我们提供了这些模型在很宽的温度范围内的汽液饱和性质。总体而言，我们观察到系统大小和边界条件的选择对计算性质有不可忽视的影响，特别是在高温下。此外，我们发现巨正则 MC 模拟和等温等压扩展温度系综 MC 模拟的组合提供了一种计算离子液体汽液饱和性质的高效计算方法。
