Fraccarollo Alberto, Canti Lorenzo, Marchese Leonardo, Cossi Maurizio
Dipartimento di Scienze e Innovazione Tecnologica (DISIT), Università del Piemonte Orientale , via T. Michel 11, 15100 Alessandria, Italy.
J Chem Theory Comput. 2017 Apr 11;13(4):1756-1768. doi: 10.1021/acs.jctc.6b01021. Epub 2017 Mar 7.
The force fields used to simulate the gas adsorption in porous materials are strongly dominated by the van der Waals (vdW) terms. Here we discuss the delicate problem to estimate these terms accurately, analyzing the effect of different models. To this end, we simulated the physisorption of CH, CO, and Ar into various Al-free microporous zeolites (ITQ-29, SSZ-13, and silicalite-1), comparing the theoretical results with accurate experimental isotherms. The vdW terms in the force fields were parametrized against the free gas densities and high-level quantum mechanical (QM) calculations, comparing different methods to evaluate the dispersion energies. In particular, MP2 and DFT with semiempirical corrections, with suitable basis sets, were chosen to approximate the best QM calculations; either Lennard-Jones or Morse expressions were used to include the vdW terms in the force fields. The comparison of the simulated and experimental isotherms revealed that a strong interplay exists between the definition of the dispersion energies and the functional form used in the force field; these results are fairly general and reproducible, at least for the systems considered here. On this basis, the reliability of different models can be discussed, and a recipe can be provided to obtain accurate simulated adsorption isotherms.
用于模拟多孔材料中气体吸附的力场主要由范德华（vdW）项主导。在此，我们讨论准确估算这些项这一微妙问题，分析不同模型的影响。为此，我们模拟了CH、CO和Ar在各种无铝微孔沸石（ITQ - 29、SSZ - 13和硅沸石 - 1）中的物理吸附，将理论结果与精确的实验等温线进行比较。力场中的vdW项根据自由气体密度和高水平量子力学（QM）计算进行参数化，比较了评估色散能的不同方法。特别地，选择具有合适基组的MP2和带半经验校正的DFT来近似最佳QM计算；在力场中使用Lennard - Jones或Morse表达式来包含vdW项。模拟等温线与实验等温线的比较表明，色散能的定义与力场中使用的函数形式之间存在强烈的相互作用；至少对于此处考虑的系统，这些结果相当普遍且可重复。在此基础上，可以讨论不同模型的可靠性，并提供一种方法来获得准确的模拟吸附等温线。
