Vlugt T J H, García-Pérez E, Dubbeldam D, Ban S, Calero S
Process & Energy Laboratory, Delft University of Technology, Leeghwaterstraat 44, 2628CA Delft, The Netherlands, Department of Physical, Chemical, and Natural Systems, University Pablo de Olavide, Ctra. Utrera km 1, 41013 Sevilla, Spain, Chemical and Biological Engineering Department, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, and Condensed Matter and Interfaces, Utrecht University, P.O. Box 80000, 08 TA Utrecht, The Netherlands.
J Chem Theory Comput. 2008 Jul;4(7):1107-18. doi: 10.1021/ct700342k.
Molecular simulations are an important tool for the study of adsorption of hydrocarbons in nanoporous materials such as zeolites. The heat of adsorption is an important thermodynamic quantity that can be measured both in experiments and molecular simulations, and therefore it is often used to investigate the quality of a force field for a certain guest-host (g - h) system. In molecular simulations, the heat of adsorption in zeolites is often computed using either of the following methods: (1) using the Clausius-Clapeyron equation, which requires the partial derivative of the pressure with respect to temperature at constant loading, (2) using the energy difference between the host with and without a single guest molecule present, and (3) from energy/particle fluctuations in the grand-canonical ensemble. To calculate the heat of adsorption from experiments (besides direct calorimetry), only the first method is usually applicable. Although the computation of the heat of adsorption is straightforward for all-silica zeolites, severe difficulties arise when applying the conventional methods to systems with nonframework cations present. The reason for this is that these nonframework cations have very strong Coulombic interactions with the zeolite. We will present an alternative method based on biased interactions of guest molecules that suffers less from these difficulties. This method requires only a single simulation of the host structure. In addition, we will review some of the other important issues concerning the handling of these strong Coulombic interactions in simulating the adsorption of guest molecules. It turns out that the recently proposed Wolf method ( J. Chem. Phys. 1999, 110 , 8254 ) performs poorly for zeolites as a large cutoff radius is needed for convergence.
分子模拟是研究烃类在纳米多孔材料（如沸石）中吸附的重要工具。吸附热是一个重要的热力学量，既可以在实验中测量，也可以在分子模拟中测量，因此它常被用于研究特定客体 - 主体（g - h）体系的力场质量。在分子模拟中，沸石中的吸附热通常采用以下方法之一计算：（1）使用克劳修斯 - 克拉佩龙方程，该方程需要在恒定负载下压力对温度的偏导数；（2）使用存在单个客体分子和不存在单个客体分子时主体的能量差；（3）从巨正则系综中的能量/粒子涨落计算。要从实验中计算吸附热（直接量热法除外），通常只有第一种方法适用。尽管对于全硅沸石来说，吸附热的计算很简单，但将传统方法应用于存在非骨架阳离子的体系时会出现严重困难。原因是这些非骨架阳离子与沸石有非常强的库仑相互作用。我们将提出一种基于客体分子偏置相互作用的替代方法，该方法受这些困难的影响较小。此方法只需要对主体结构进行一次模拟。此外，我们将回顾在模拟客体分子吸附时处理这些强库仑相互作用的其他一些重要问题。结果表明，最近提出的沃尔夫方法（《化学物理杂志》1999年，110卷，8254页）对于沸石效果不佳，因为收敛需要较大的截断半径。
