Direct, real-space solution of zeolite framework crystal structures by simulated annealing has been explored as an alternative to conventional powder diffraction or model-building methods. The method, as well as its success in predicting the framework structures of known zeolites, is described in detail. Data taken as input to the method are unit cell dimensions, symmetry, and framework density. The general geometrical characteristics of the 4-connected framework structures of zeolite materials are captured by a figure of merit that contains terms based on T-T distances (T = tetrahedral species, Si or Al etc.), T-T-T angles and average angles, degree of T-atom coordination, appearance of 3-connectedness in projection, and cylindrical or spherical pore size. Test solutions of 64 known zeolite structures with 6 or fewer unique T-atoms give a successful result in 57 cases. Low-symmetry systems, in particular, tend to give rise to large numbers of hypothetical 4-connected structures that satisfy the geometrical considerations, and in total, more than 5000 hypothetical structures have been produced. The observed structure usually ranks among those with the lower values of the figure of merit. Incorporation of a sample-specific contribution to the figure of merit based on the degree to which the model matches a target powder diffraction pattern improves the success of the method. This additional term almost invariably causes the observed, known structure to have the lowest value of the figure of merit, and it is thus a great aid in practical structure solution.
