Single and Multiple Rings, and Cages in SiO$_{x}$ Clusters

Theoretical studies on the geometry, electronic structure and stability of Si$_{n}$O$_{m}$ clusters have been carried out within a gradient corrected density functional formalism. It is shown that the ground states of small Si$_{n}$O$_{n}$ clusters containing upto 4 units are single rings. The first Si-Si bond appears at Si$_{5}$O$_{5}$, and starting at this size, the elementary rings begin to assemble into multiple rings that eventually lead to cages. The ground state structures at larger sizes have a central core of pure Si atoms decorated by outer shell of SiO units. An analysis of the fragmentation patterns shows that Si$_{7}$O$_{7}$ and Si$_{10}$O$_{10}$ are particularly stable species. The results of our investigations on the Si$_{n}$O$_{n-1}$ and Si$_{n}$O$_{n+1}$ species will also be presented. In particular, we will examine possible reaction mechanisms that could lead to the formation of SiO$_{2}$ from SiO molecules in interstellar space.