Geometrical and electronic structures of small Co–Mo nanoclusters

Abstract

The geometries, energetics and electronic structures of Co₁₃, Mo₁₃, Co₁₂Mo and Mo₁₂Co clusters are systematically investigated by using the first principles method combined with a genetic algorithm. A new candidate is found for the ground-state geometry of Mo₁₃. Compared to the ground-state geometry of Co₁₃ possessing high stability, there are many isomers energetically closer to the ground-state of Mo₁₃. The relatively high stability of the pure Co₁₃ can be reduced by doping, but the isomerization near the ground-state of the pure Mo₁₃ can be suppressed by doping. With respect to that of the central doping Mo atom in the high symmetric close-packed geometry, there are significantly more d electrons near the Fermi energy of the Mo atom in the ground-state Co₁₂Mo cluster and as a result the d–d hybridization between the doped atom and the matrix is significantly enhanced. In contrast, compared to the excited structure with a relatively higher energy, the d–d hybridization near the Fermi energy between the doped atom and the matrix of the ground-state Mo₁₂Co cluster is significantly decreased, which implies that the d–d hybridization near the Fermi energy between the doped atom and the matrix is strongly influenced by the component ratio and geometry of the cluster, and the competition between them can have a crucial impact on the catalytic property of the mixed cluster. An explanation is proposed for the excellent catalytic abilities of the Co–Mo alloy nanoclusters with approaching component ratios in the catalytic growth of carbon nanotubes.