Patet Ryan E, Caratzoulas Stavros, Vlachos Dionisios G
Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA.
Phys Chem Chem Phys. 2016 Sep 21;18(37):26094-26106. doi: 10.1039/c6cp03266d.
We have explored mechanically embedded three-layer QM/QM/MM ONIOM models for computational studies of binding in Al-substituted zeolites. In all the models considered, the high-level-theory layer consists of the adsorbate molecule and of the framework atoms within the first two coordination spheres of the Al atom and is treated at the M06-2X/6-311G(2df,p) level. For simplicity, flexibility and routine applicability, the outer, low-level-theory layer is treated with the UFF. We have modelled the intermediate-level layer quantum mechanically and investigated the performance of HF theory and of three DFT functionals, B3LYP, M06-2X and ωB97x-D, for different layer sizes and various basis sets, with and without BSSE corrections. We have studied the binding of sixteen probe molecules in H-MFI and compared the computed adsorption enthalpies with published experimental data. We have demonstrated that HF and B3LYP are inadequate for the description of the interactions between the probe molecules and the framework surrounding the metal site of the zeolite on account of their inability to capture dispersion forces. Both M06-2X and ωB97x-D on average converge within ca. 10% of the experimental values. We have further demonstrated transferability of the approach by computing the binding enthalpies of n-alkanes (C1-C8) in H-MFI, H-BEA and H-FAU, with very satisfactory agreement with experiment. The computed entropies of adsorption of n-alkanes in H-MFI are also found to be in good agreement with experimental data. Finally, we compare with published adsorption energies calculated by periodic-DFT for n-C3 to n-C6 alkanes, water and methanol in H-ZSM-5 and find very good agreement.
我们探索了机械嵌入的三层QM/QM/MM ONIOM模型，用于铝取代沸石中结合作用的计算研究。在所有考虑的模型中，高级理论层由吸附质分子以及铝原子前两个配位球内的骨架原子组成，并在M06 - 2X/6 - 311G(2df,p)水平下处理。为了简单、灵活和常规适用性，外层的低级理论层采用UFF处理。我们对中间层进行了量子力学建模，并研究了HF理论以及三种DFT泛函B3LYP、M06 - 2X和ωB97x - D在不同层大小和各种基组下（有无BSSE校正）的性能。我们研究了16种探针分子在H - MFI中的结合情况，并将计算得到的吸附焓与已发表的实验数据进行了比较。我们已经证明，HF和B3LYP由于无法捕捉色散力，不足以描述探针分子与沸石金属位点周围骨架之间的相互作用。M06 - 2X和ωB97x - D平均收敛到实验值的约10%以内。我们通过计算正构烷烃（C1 - C8）在H - MFI、H - BEA和H - FAU中的结合焓，进一步证明了该方法的可转移性，与实验结果非常吻合。还发现正构烷烃在H - MFI中的计算吸附熵与实验数据也吻合良好。最后，我们将计算结果与已发表的通过周期性DFT计算得到的H - ZSM - 5中正丙烷到正己烷、水和甲醇的吸附能进行了比较，发现吻合度非常好。
