The interactions between metal–organic frameworks (MOFs) and adsorbates have been increasingly predicted and studied by computer simulations, particularly by Grand-Canonical Monte Carlo (GCMC), as this method enables comparing the results with experimental data and also provides a degree of molecular level detail that is difficult to obtain in experiments. The assignment of atomic point charges to each atom of the framework is essential for modelling Coulombic interactions between the MOF and the adsorbate. Such interactions are important in adsorption of polar gases like water or carbon dioxide, both of which are central in carbon capture processes. The aim of this work is to systematically investigate the effect of varying atomic point charges on adsorption isotherm predictions, identify the underlying trends, and based on this knowledge to improve existing models in order to increase the accuracy of gas adsorption prediction in MOFs. Adsorption isotherms for CO₂ and water in several MOFs were generated with GCMC, using the same computational parameters for each material except framework point charge sets that were obtained through a wide range of computational approaches. We carried out this work for 6 widely studied MOFs; IRMOF-1, MIL-47, UiO-66, CuBTC, Co-MOF-74 and SIFSIX-2-Cu-I. We included both MOFs with and without open metal sites (OMS), specifically to investigate whether this property affects the predicted adsorption behaviour. Our results show that point charges obtained from quantum mechanical calculations on fully periodic structures are generally more consistent and reliable than those obtained from either cluster-based QM calculations or semi-empirical approaches. Furthermore, adsorption in MOFs that contain OMS is much more sensitive to the point charge values, with particularly large variability being observed for water adsorption in such MOFs. This suggests that particular care must be taken when simulating adsorption of polar molecules in MOFs with open metal sites to ensure that accurate results are obtained.

中文翻译：

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原子点电荷对金属有机骨架中CO 2和水的吸附等温线的影响

金属-有机骨架（MOFs）与被吸附物之间的相互作用已通过计算机模拟，尤其是大正则蒙特卡洛法（GCMC）的计算机模拟得到了越来越多的预测和研究，因为该方法能够将结果与实验数据进行比较，并提供一定程度的分子分析。在实验中难以获得的详细级别。将原子点电荷分配给框架的每个原子对于模拟MOF与被吸附物之间的库仑相互作用至关重要。这种相互作用对于吸附极性气体（例如水或二氧化碳）非常重要，而这两种气体在碳捕获过程中都至关重要。这项工作的目的是系统地研究变化的原子点电荷对吸附等温线预测的影响，确定潜在的趋势，并基于此知识来改进现有模型，以提高MOF中气体吸附预测的准确性。一氧化碳的吸附等温线₂用GCMC生成了几个MOF中的水和水，每种材料使用相同的计算参数，但通过各种计算方法获得的构架点电荷集除外。我们针对6个受到广泛研究的MOF进行了这项工作；IRMOF-1，MIL-47，UiO-66，CuBTC，Co-MOF-74和SIFSIX-2-Cu-I。我们包括有和没有金属开放位点（OMS）的MOF，专门研究这种性质是否会影响预期的吸附行为。我们的结果表明，与从基于簇的QM计算或半经验方法获得的电荷相比，从全周期结构的量子力学计算获得的点电荷通常更加一致和可靠。此外，包含OMS的MOF中的吸附对点电荷值更为敏感，在此类MOF中观察到的水吸附变化特别大。这表明在模拟具有开放金属位点的MOF中极性分子的吸附时必须格外小心，以确保获得准确的结果。