SURFACE-RECONSTRUCTION-INDUCED GEOMETRIES OF SI CLUSTERS

We discuss a generalization of the surface-reconstruction arguments fo r the structure of intermediate-size Si clusters, which leads to model geometries for the sizes 33, 39 (two isomers), 45 (two isomers), 49 ( two isomers), 57, and 61 (two isomers). The common feature in all thes e models is a structure that closely resembles the most stable reconst ruction of Si surfaces, surrounding a core of bulklike tetrahedrally b onded atoms. We investigate the energetics and the electronic structur e of these models through first-principles density-functional theory c alculations. These models may be useful in understanding experimental results on the reactivity of Si clusters and their shape as inferred f rom mobility measurements.