Energetics and structures of the initial stages of nucleation of (SiO2)N species: possible routes to highly symmetrical tetrahedral clusters

Abstract

A detailed survey of the low energy isomer spectrum of (SiO₂)_N, N = 6–10, 13, 16 has been performed using interatomic potential based global optimisations refined via high-level density functional calculations. Within these spectra, including many isomers reported for the first time, structurally and energetically viable pathways for the initial stages of silica cluster growth through SiO₂ nucleation are identified. The role of the exceptionally stable (SiO₂)₈ ground state “magic” cluster is highlighted in the possible formation of highly symmetric fully tetrahedral clusters of size (SiO₂)₁₀ and (SiO₂)₁₆. These clusters are found to form a part of a natural (SiO₂)_NN = 7, 10, 13, 16 sequence together with the C_3v ground states for (SiO₂)₇ and (SiO₂)₁₃. The fully tetrahedral clusters are argued to be likely relatively long-lived metastable species in the process of gas phase SiO₂ nucleation due to the manner of their termination. It is speculated that larger tetrahedral (SiO₂)₄₀ clusters may exhibit porous structures.