Zeolite Structure Prediction and the Identification of Useful Synthetic Targets M. M. J. Treacy, Arizona State University, Tempe, Arizona We have found that almost all real zeolite frameworks exhibit a flexibility window, where the rigid SiO4 tetrahedra can rotate about the corner-shared linkages without causing any stress. This flexibility may be an important topological property allowing us to tell which hypothetical zeolite frameworks are plausible. We have found that this flexibility is a consequence of the perfect balance between coordinate degrees of freedom and constraints, plus, importantly, the presence of periodicity. Ideal Zeolite Frameworks when heated, experience a kinetic inflationary force that causes them to adopt the maximum volume state within the flexibility window (central figure). This guarantees maximum configurational entropy. No electrostatic repulsive potentials are needed to maximize volume.