(197n) Computational Model of Defect Propagation Mechanisms in ZIF-8

Zeolitic imidazolate frameworks (ZIFs) are a subset of metal organic frameworks (MOFs) composed of Zn centers connected by imidazolate ligands. Although ZIFs shown good thermal stability, they are known to degrade in humid and acidic environments. Most previous work has focused on describing single bond-breaking defect events and there is not a good understanding for how these localized defects propagate throughout the bulk to result in structural collapse. However, understanding the propagation mechanism is a crucial step in developing guiding principles (descriptors) for evaluating how performance of defective ZIFs deviates from that of the pristine material. Here we use density functional theory (DFT) to systematically investigate formation of multiple water and H₂SO_X induced defects in bulk ZIF-8. First, we examine the energetics of defect proximity and conclude that clustering is favourable. Then we exhaustively consider all nearby defects to determine which conditions and configurations most strongly predict adjacent defect formation. Finally, we demonstrate that our propagation model describes successive defect formation which is not only favourable, but also compatible with experimental analysis of degraded ZIF-8 structures.