Partially reactive force field for the UiO-66 metal-organic framework

TL;DR

This paper introduces nb-UiO-FF, a partially reactive force field for modeling UiO-66 MOF, capturing structural, mechanical, and defect formation features, and enabling studies of its self-assembly and defect dynamics.

Contribution

The development of nb-UiO-FF, a novel force field incorporating node-ligand reactivity and anisotropic charge distribution for accurate simulation of UiO-66 MOF.

Findings

Reproduces structural features of UiO-66 and UiO-67

Accurately models mechanical properties and stability with defects

Identifies thermodynamically and kinetically favored structural motifs during node-ligand binding

Abstract

UiO-66 is the most widely studied metal-organic framework (MOF), on account of its structural tunability given by its capacity of sustaining high amounts of point defects in its structure. Its synthesis mechanism is largely unknown, with only a few works mostly focused on the formation of the Zr-oxide cluster. In this work, a partially reactive force field to model UiO-66, nb-UiO-FF, is introduced. This force field incorporates node--ligand reactivity via a Morse potential and the introduction of dummy atoms to reproduce the anisotropic charge distribution of the Zr atoms in the node. nb-UiO-FF reproduces structural features of both UiO-66 and its isoreticular analog UiO-67, mechanical properties and framework stability with or without defects, activated or filled with N,N-dimethylformamide or ethanol. The force field is further employed within a molecular dynamics scheme to study the early stages of solvothermal node--ligand binding. Transient structural motifs both thermodynamically and kinetically favored are identified. This force field enables studying the self-assembly of UiO-66, as well as the formation of its point defects.