Structure and stability ofSi45clusters: A generalized tight-binding molecular-dynamics approach

We compare the relative stabilities of all the proposed low-energy isomers of the ${\mathrm{Si}}_{45}$ cluster using a generalized tight-binding molecular-dynamics scheme. This technique has been used earlier to obtain good agreement with ab initio results for small silicon clusters and shown to be transferable to bulk solids. In agreement with local-density-approximation-based results, we find the lowest-energy structure to consist of two concentric shells with a highly distorted fullerenelike outer layer, and a highly coordinated inner core with a central atom. Additionally, we have found several nearly isoenergetic structures in which the inner core has no central atom. This suggests that structural transition to bulklike coordination might occur for significantly larger clusters.