Structural and electronic properties of Al12X+ (X=C, Si, Ge, Sn, and Pb) clusters

Using the first-principles method with the generalized gradient approximation, the authors have studied the structural and electronic properties of Al12X+ (X=C, Si, Ge, Sn, and Pb) clusters in detail. The ground state of Al12C+ is a low symmetry C-s structure instead of an icosahedron. However, the Si, Ge, Sn, and Pb atom doped cationic clusters favor icosahedral structures. The ground states for Al12Si+ and Al12Ge+ are icosahedra, while the C-5 nu structures optimized from an icosahedron with a vertex capped by a tetravalent atom have the highest binding energy for Al12Sn+ and Al12Pb+ clusters. The I-h structure and the C-5 nu structure are almost degenerate for Al12Ge+, whose binding energy difference is only 0.03 eV. The electronic properties are altered much by removing an electron from the neutral cluster. The binding strength of a valence electron is enhanced, while the binding energy of the cluster is reduced much. Due to the open electronic shell, the band gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital are similar to 0.3 eV for the studied cationic clusters.