Metal-organic frameworks (MOFs) are a class of porous materials composed of metal clusters, also known as secondary building units (SBUs) and organic linkers arranged in 1-, 2-, or 3-dimension networks. Several MOFs have shown to be able to readily adsorbed guest species in their pores, which has been exploited for several technological applications, including, but not limited to, gas storage, water harvesting, and drug delivery. From a modeling perspective, realistic simulations of guest adsorption in MOFs are particularly challenging. While ab initio methods can, in principle, provide an accurate representation of guest-framework interactions, their computational cost effectively precludes sufficiently long simulations to monitor the entire adsorption process. On the other hand, conventional force fields for MOFs are computationally efficient, but display limited accuracy and effectively lack any predictive power due to the absence of the flexibility of the framework and guest-framework polarization effects.<br/>Here we present a novel theoretical/computational approach for MOF simulations which account for both framework flexibility and polarization effects. We present results for water adsorption in NU-1500-Cr, where the water interactions are described by our data-driven, many-body MB-pol model that has been shown to correctly predict the properties of water from gas-phase clusters to liquid water and ice. Besides monitoring the evolution of structural and thermodynamic properties of water inside the NU-1500-Cr pores as a function of relative humidity, we also simulate the corresponding infrared spectra in order to provide molecular insights into the adsorption process and allow direct comparisons with experiment. As a second example of our theoretical/computational approach, we also present results for the adsorption of fluorocarbon molecules in Fe-HAF-2, a recently synthesized MOF.

Computational modeling of guest molecule adsorption in metal-organic frameworks

ACS Spring 2022

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