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

## TL;DR

A new force field model improves simulations of gas adsorption in metal-organic frameworks with open metal sites, enhancing accuracy for applications like air capture and water harvesting.

## Contribution

A transferable force field based on the 12–6–4 Lennard-Jones potential is developed to model host–guest interactions involving open metal sites.

## Key findings

- The new force field accurately models host–guest binding energetics and gas adsorption isotherms in various MOFs.
- The approach shows excellent transferability across different open metal site-containing MOFs like MOF-74 and Cu-BTC.
- The model incorporates charge–induced dipole interactions parametrized from density functional theory data.

## Abstract

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.