Structure and properties of small silicon and aluminum clusters

Small Si_n and Al_n clusters (n = 3–10) were studied with the semiempirical molecular orbital method (MO) method SINDO1. For each n, various structures were optimized to determine the most stable structure. To obtain good qualitative agreement with available ab initio calculations d orbitals had to be omitted from the basis set. Both silicon and aluminum tend to build three-dimensional structures rather than two- or one-dimensional structures, except for n = 3 or 4. The structure growth was studied by approaching various sites of stable structures with one or more atoms. It was found that silicon and aluminum exhibit different structure growth, and consequently, different most-stable structures. Ionization potentials, HOMO -LUMO energy differences, binding energies per atom, and average atomic valencies are presented.