Observed electron density distributions for the silica polymorphs coesite and stishovite will be analyzed in terms of their topographical features. Critical points and bond paths for these distributions will be located by calculating gradient vector maps and regions of bonded and nonbonded densities will be located by calculating Laplacian relief maps. An analysis of the maps will pinpoint regions that are susceptible to electrophilic and nucleophilic attack, information that is important to understanding mechanisms of surface reactions, transition states and catalytic reactions in zeolites. The method will also be examined as a tool for monitoring phase transformations. It is anticipated that the calculations will generate new zeolite structure types, materials of considerable interest in the petrochemical industry as solid state acids and catalysts for producing high-grade gasoline from coal gases and molecular sieves for beneficiating petroleum products and for serving as environmental filters.
