Combining Coarse-Grained Reactive Molecular Dynamics with an Enhanced-Sampling Method for MFI Zeolite Crystallization

The crystallization kinetics of zeolites (e.g., ZSM-5) have scientific and industrial significance for chemical engineering. However, their nucleation mechanism at the microscopic level remains unclear because nucleation is the rare event in the complex multicomponent system. Here, we developed a coarse-grained reactive zeolite assembly model (CG-ReZAM) that captures the dynamic microscopic details of silicate polymerization with organic structure-directing agents (OSDAs). Taking the MFI-type zeolite as the case study, the four characteristic stages of silicate polymerization are reproduced: oligomerization, ring formation, cluster aggregation, and aging. We further introduced the cluster-weighted root-mean-square deviation (cRMSD) as a collective variable (CV) combined with the ratcheting scheme to enhance sampling of nucleation events. This approach accelerates the formation of ordered MFI-type zeolites within feasible time scales and reveals the full transformation pathway from amorphous aggregates to ordered crystals. During growth, we observed the ordered arrangements of tetrapropylammonium (TPA⁺) cations within the growing framework, confirming their structure-directing role in stabilizing long-range order. The critical nucleus size extracted from mean first-passage time (MFPT) analysis is consistent with experimental observations and further demonstrates the reliability of our method of combining our CG-ReZAM with an enhanced-sampling strategy for zeolite crystallization. Overall, this framework offers valuable theoretical insights into supporting the rational design of zeolite materials for applications in catalysis and separation.