Structural and electronic properties of Al12 X+ (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 Al12 X+ (X=C, Si, Ge, Sn, and Pb) clusters in detail. The ground state of Al12 C+ is a low symmetry Cs structure instead of an icosahedron. However, the Si, Ge, Sn, and Pb atom doped cationic clusters favor icosahedral structures. The ground states for Al12 Si+ and Al12 Ge+ are icosahedra, while the C5 structures optimized from an icosahedron with a vertex capped by a tetravalent atom have the highest binding energy for Al12 Sn+ and Al12 Pb+ clusters. The Ih structure and the C5 structure are almost degenerate for Al12 Ge+, 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 ∼0.3 eV for the studied cationic clusters.