Structures and energies of SiO2 clusters

We have employed extensive configurational searches for numerical characterization of neutral (SiO2)(n) clusters in their mechanically stable forms, i.e., at local potential energy minima. These calculations have used additive pair interactions derived by Tsuneyuki et al., supplemented with small-distance configurational constraints. A nearly complete catalog of structures and energies has been obtained for 1 less than or equal to n less than or equal to 4, and we also report the most stable clusters found for 5 less than or equal to n less than or equal to 8, as well as n = 18. Also a few key sequences of metastable oligomers have been examined. Although the results illustrate the basic tendency toward tetrahedral coordination of silicons by oxygens, none of the stable clusters structurally resemble any of the known crystalline SiO2 polymorphs. The n 18 results suggest that the surfaces of extended crystalline or glassy SiO2 phases may exhibit anomalously coordinated silicons with formal valences +3 and +5.