The first observations that the flexibility of framework materials could be heavily influenced by crystal size, shape, di-mensionality or morphology are not recent. The microscopic mechanism for such dependency was originally not fully understood, and remains in many cases a subject of conjecture, because spatially-resolved characterization of these systems is difficult to achieve. Moreover, atomistic-level molecular simulation approaches of finite crystals are challenging as most computational approaches use periodic boundary conditions, which are incompatible with the study of finite-size systems.