Local topology of silica networks

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Abstract
Model-building algorithms based on self-assembly according to local rules have been devised, which permit rapid assembly of vertex-sharing tetrahedral network structures. These have been applied to investigation of the topological properties of crystalline and amorphous network silicas. Local assembly rules for the six compact crystalline silica tetrahedral network polymorphs have been formulated which reproduce the fundamental topologies of the polymorphs and permit investigation of the range of displacive modifications. Amorphous networks can be generated by application of deviant rules, and two are explored on the basis of modifications of quartz and cristobalite assembly rules. The global topologies of the crystalline polymorphs are found to be fully embodied in their local clusters, which consists of sets of irreducible rings and associated tetrahedra. The local clusters provide a local description of structure that serves as an alternative to the unit cell of crystallography and is applicable to non-periodic structures. The availability of the full adjacency matrix and tetrahedron coordinates, for generated crystalline and amorphous assemblages alike, provides ready access to all local clusters, bond-angle distributions and partial radial correlations.

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