Metal-encapsulated fullerenelike and cubic caged clusters of silicon

We report metal-encapsulated caged clusters of silicon from ab initio pseudopotential plane wave calculations using generalized gradient approximation for the exchange-correlation energy. Depending upon the size of the metal (M) atom, silicon forms fullerenelike M@Si-16, M = Hf Zr, and cubic M@Si-14, M = Fe, Ru, Os, caged clusters. The embedding energy of the M atom is approximate to 12 eV due to strong M-SI interactions that make the cage compact. Bonding in these clusters is predominantly covalent and the highest-occupied-lowest-unoccupied molecular orbital gap is approximate to1.5 eV. However, an exceptionally large gap (2.35 eV) is obtained for Ti@Si-16 Frank-Kasper polyhedron. Interaction between these clusters is weak, making them attractive for cluster-assembled materials.