A Transferable Force Field for Simulating Adsorption in Metal–Organic Frameworks with Open Metal Sites Based on the 12–6–4 Lennard-Jones Potential

Metal–organic frameworks (MOFs) that contain coordinatively
unsaturated open metal sites (OMSs) provide strong host–guest
interactions, making them promising sorbents for low-concentration
gas adsorption applications such as direct air capture and atmospheric
water harvesting. However, accurately modeling host–guest interactions
involving OMSs remains challenging for classical force fields (FFs)
based on the 12–6 Lennard–Jones (LJ) potential, as the
polarization effect of the guest molecule induced by the positively
charged OMS is not considered. Here, we introduce an FF based on the
12–6–4 LJ potential, which incorporates charge–induced
dipole interactions and is parametrized against a diverse set of host–guest
potential energy surfaces (PESs) obtained from density functional
theory (DFT). The resulting FF, trained on a generic trimetallic cluster,
performs well in both host–guest binding energetics and gas
adsorption isotherms across different OMS-containing MOFs, including
MOF-74 series and Cu-BTC. These results highlight the excellent transferability
of our approach and its potential to enhance the accuracy and robustness
of high-throughput MOF discovery workflows, particularly for gas adsorption
and separation in large and diverse MOF databases.