VIBRATIONAL SIGNATURES FOR LOW-ENERGY INTERMEDIATE-SIZED SI CLUSTERS

We report low-energy focally stable structures for the clusters Si-20 and Si-21. The structures were obtained by performing geometry optimiz ations within the local density approximation. Our calculated binding energies for these clusters are larger than any previously reported fo r this size regime. To aid in the experimental identification of the s tructures, we have computed the full vibrational spectra of the cluste rs, along with the Raman and IR activities of the various modes using a recently developed first-principles technique. These represent, to o ur knowledge, the first calculations of Raman and IR spectra for Si cl usters of this size.