The high throughput construction and analysis of bilayers of tetrahedra

Abstract

A method for generating significant numbers of network configurations is developed appropriate to bilayers of systems such as SiO2, GeO2, and aluminosilicates. The presence of a mirror plane allows the bilayer structures to exactly map onto a two-dimensional network of three-coordinate nodes (equivalent to a percolating network of rings). A bond switching algorithm is employed to generate a range of disordered (amorphous) network topologies (characterized by the ring size distribution and the nearest-neighbor connectivities, as measured by the Aboav–Weaire Law and assortativity). Bilayer configurations are generated from these networks, and energy minimizations are performed using a hierarchy of potential models: a purely harmonic potential, a harmonic potential with an inter-tetrahedral repulsive term, a rigid-ion model, and a polarizable-ion model. The harmonic potential shows a flexibility window whose extent depends on the spatial extent of the inter-tetrahedral repulsive term. The window becomes less well-defined for higher level (rigid-ion and polarizable-ion) models. Distortions of the bilayer networks are characterized with reference to both the ideal (hexagonal) crystal and the amorphous networks. In addition, a “pore evaporation” algorithm is developed and used to generate a range of potential zeolitic bilayer networks. These networks, which are ordered but contain significant numbers of non-hexagonal rings, provide a useful contrast to the disordered networks.