Enabling Computational Design of ZIFs Using ReaxFF

Classical force fields have been broadly used in studies of metal-organic framework crystals. However, processes involving bond breaking or forming are prohibited due to the nonreactive nature of the potentials. With emerging trends in the study of zeolitic imidazolate frameworks (ZIFs) that include glass formation, defect engineering, and chemical stability, enhanced computational methods are needed for efficient computational screening of ZIF materials. Here, we present simulations of three ZIF compounds using a ReaxFF reactive force field. By simulating the melt-quench process of ZIF-4, ReaxFF can reproduce the atomic structure, density, thermal properties, and pore morphology of the glass formed (a_gZIF-4), showing remarkable agreement with experimental and first-principles molecular dynamics results. The predictive capability of ReaxFF is further exemplified in the melting of ZIF-62, where the balancing of electronic and steric effects of benzimidazolate yields a lower T_m. On the basis of the electron-withdrawing effect of the -NO₂ group, ReaxFF simulations predict that ZIF-77 has an even lower T_m in terms of Zn-N interaction, but its low chemical stability makes it unsuitable as a glass former. Because of its low computational cost and transferability, ReaxFF will enable the computational design of ZIF materials by accounting for properties associated with disorder/defects.