A structural model for intermediately sized Si clusters was proposed which was able to generate unique structures without any dangling bonds. The model consisted of a bulk-like core of 5 atoms, surrounded by a fullerene-like surface. Reconstruction of the ideal fullerene geometry resulted in the formation of crown atoms, surrounded by -bonded dimers. The model yielded unique structures for Si33, Si39 and Si45 centers without any dangling bonds, and hence explained why these clusters were the least reactive with regard to the chemisorption of NH3. Experimentally observed reagent-specific chemisorption reactivities were explained on the basis of the electronic structures of the reagents.

J.Pan, M.V.Ramakrishna: Physical Review B, 1994, 50[20], 15431-4