Metal-encapsulated icosahedral superatoms of germanium and tin with large gaps: Zn@Ge ₁₂ and Cd @Sn ₁₂

Metal (M)-encapsulated clusters of Ge and Sn, Zn@Ge ₁₂ and Cd@Sn ₁₂ , are obtained from total energy calculations using ab initio pseudopotential plane wave method and generalized gradient approximation for the exchange-correlation energy. These have perfect icosahedral symmetry and large highest occupied-lowest unoccupied molecular orbital gap of about 2 eV. It lies in the optical region and makes these species attractive for cluster assembled optoelectronic materials. Calculations on silicon clusters doped with Be show a different behavior.