Nonbonded Zr<sup>4+</sup> and Hf<sup>4+</sup> Models for Simulations of Condensed Phase Metal–Organic Frameworks
Hao Su, Mårten S. G. Ahlquist
Abstract
Recently, the practical applications of tetravalent metal-based metal–organic frameworks (MOFs) have been drawing increasing attention due to their excellent stability and varied functionality. Understanding the behavior of MOFs at the atomic level is important for their rational design and postsynthetic optimization. In classical simulations, the cationic dummy atom model, where the charge of the metal ion is distributed to surrounding dummy particles, has shown robustness in providing the appropriate coordination geometry while retaining the flexibility in the metal ligand interaction. Here, we present a set of eight-coordinated tetravalent metal (Zr4+, Hf4+) dummy model force fields with 12-6-4 type Lennard–Jones potential for describing ion-induced dipole interactions. This model can reproduce both the experimental solvation free energy of the bare ion and good metal–ligand distances and has been validated as useful and transferable among MOFs with the same metal-core topology. The model is inherently modular since nodes and linkers are independently parametrized. It was tested with three different solvents which all led to stable structures. It also was been further validated with different metal node structures and different linkers, Zr/Hf mixed MOFs, and defects containing MOFs. Since the model is nonbonded, the process of metal–ligand substitutions could be studied. The flexibility of the model makes its applicability to chemical problems broad.