Modeling CO2 Adsorption in Flexible MOFs with Open Metal Sites via Fragment-Based Neural Network Potentials

02 May 2025, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Metal-organic frameworks (MOFs) with open metal sites (OMS) are among the most promising porous materials for gas adsorption and separation, owing to their strong and selective interactions with guest molecules. However, simulating adsorption in such systems with high accuracy and efficiency remains a key challenge due to the need to model complex guest–MOF interactions and framework flexibility. Classical force fields often lack the precision to capture these effects, while ab initio methods are computationally prohibitive for large-scale, long-timescale simulations. In this work, we develop a neural network potential (NNP) trained on highly accurate DFT (PBE-D4/def2-TZVP) level data derived from a single representative fragment of the Mg-MOF-74 framework, a prototypical OMS-containing MOF, with CO2 molecules. Despite the limited training domain, the NNP accurately captured both intra- and intermolecular interactions in the CO2–Mg-MOF-74 system, including those involving the open metal sites. We integrated this NNP into a hybrid molecular dynamic (MD) and grand canonical Monte Carlo (GCMC) simulation workflow, enabling accurate modeling of CO2 adsorption in flexible MOFs. This approach allows us accounting for both framework dynamics and complex host–guest interactions with chemical accuracy and computational efficiency. Our results highlight the crucial role of framework flexibility in adsorption behavior and demonstrate that fragment-based NNP, when combined with advanced simulation techniques, offer a powerful and efficient approach for realistically modeling adsorption processes in MOFs with open metal sites.

Supplementary materials

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Title
Modeling CO2 Adsorption in Flexible MOFs with Open Metal Sites via Fragment-Based Neural Network Potentials
Description
Details of computational methods; changes in the number of adsorbed CO2 molecules, volume, and temperature over time during flexible MD/GCMC simulations of Mg-MOF-74; training and validation loss curves; CO2 adsorption isotherms on Mg-MOF-74 from rigid GCMC simulations under different conditions; probability distributions of CO2 in Mg-MOF-74.
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