A computational investigation of copper-doped germanium and germanium clusters by the density-functional theory

The geometries, stabilities, and electronic properties of Ge-n and CuGen (n=2-13) clusters have been systematically investigated by using density-functional approach. According to optimized CuGen geometries, growth patterns of Cu-capped Ge-n or Cu-substituted Gen+1 clusters for the small- or middle-sized CuGen clusters as well as growth patterns of Cu-concaved Ge-n or Ge-capped CuGen-1 clusters for the large-sized CuGen clusters are apparently dominant. The average atomic binding energies and fragmentation energies are calculated and discussed; particularly, the relative stabilities of CuGe10 and Ge-10 are the strongest among all different sized CuGen and Ge-n clusters, respectively. These findings are in good agreement with the available experimental results on CoGe10- and Ge-10 clusters. Consequently, unlike some transition metal (TM)Si-12, the hexagonal prism CuGe12 is only low-lying structure; however, the basketlike structure is located as the lowest-energy structure. Different from some TM-doped silicon clusters, charge always transfers from copper to germanium atoms in all different sized clusters. Furthermore, the calculated highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gaps are obviously decreased when Cu is doped into the Ge-n clusters, together with the decrease of HOMO-LUMO gaps, as the size of clusters increases. Additionally, the contribution of the doped Cu atom to bond properties and polarizabilities of the Ge-n clusters is also discussed. (c) 2005 American Institute of Physics.