Structural growth sequences and electronic properties of manganese-doped germanium clusters:: MnGen (2-15)

The structural growth sequences and electronic properties of MnGen (n = 2-15) clusters have been investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). An extensive search of the lowest-energy structures was conducted by considering a number of structural isomers for each cluster size. In the ground-state structures of MnGen clusters, the equilibrium site of the Mn atom gradually moves from the convex, surface to interior sites as the Ge cluster size varies from 2 to 15. The threshold size for the formation of caged MnGen and the sealed Mn-encapsulated Ge-n structure is n = 9 and n = 10, respectively. Maximum peaks were observed for MnGen clusters at n = 3, 6, 10, 12 and 14 with the size dependent on the second-order energy difference, implying that these clusters are relatively more stable. The electronic structures and magnetic properties of MnGen in the ground-state structures are discussed. The doped Mn atom makes the HOMO-LUMO gap of the Ge-n clusters smaller, due to hybridization between the p states of the Ge atom and the d states of the Mn atom. Most of the Mn-doped Ge-n clusters carry a magnetic moment of about 1.0 mu B, except that MnGe6 and MnGe11 have a magnetic moment of about 3.0 mu B. Charge transfer between Mn and Ge was also observed.