Adsorption of Hydrocarbons in Metal-Organic Frameworks: A Force Field Benchmark on the Example of Benzene in Metal-Organic Framework 5

For the application of metal-organic frameworks (MOTs), the understanding of host-guest interactions on a molecular level is crucial, and often only theoretical methods allow such an insight. However, to obtain quantitative information from such calculations, a validation of the applied methods is indispensable. In this work we investigate for the first time the physisorption of benzene, as a probe molecule for larger guest molecules, within the matrix of MOF-5 using high-level quantum mechanical methods. The calculations reveal a large contribution of dispersion effects on the host-guest interaction. The importance of both reliable and efficient quantum mechanical techniques, which are able to properly cover these effects, is discussed. We find that in particular a double-hybrid functional together with an empirical long-range dispersion correction is an accurate and robust method for the rather large model systems. In addition, our quantum mechanical results enabled us to benchmark for the first time the performance of force fields to describe the interaction of hydrocarbons with the periodic framework. This kind of bottom-up validation of host-guest interactions strengthens the predictive power of theoretical methods in the area of MOF research.