Ab initio investigations of the transport properties of a Ge7 cluster

Based on first-principles calculations, we have systematically investigated the electrical transport properties of a Ge-7 cluster, which is respectively coupled with two kinds of atomic scale Ag(110) and Ag(100) electrodes with finite cross sections. Our results clearly suggest that, under strong cluster-electrode coupling, the equilibrium conductance of the Ge-7 cluster coupled with thin Ag nanowires takes the value of about 3 and 4 (units of G(0)=2e(2)/h) in the case of Ag(110) and Ag(100), respectively. The eigenchannel and electronic structure analyses show that, in the strong cluster-electrode coupling regime, the transport properties of Ge-7 cluster connected to thin Ag wires are very closely related to the band structure of the nanowire electrode in both equilibrium and nonequilibrium situations. Under zero bias, the number of the electrode bands crossing the Fermi level determines the number of conductance channels of the Ge-7 cluster. Therefore, for the Ag(100) electrode case, more bands crossing the Fermi energy results in a larger conductance than that in the Ag(110) case. By varying the cluster-electrode contact distances, we observe that the equilibrium conductance of the Ge-7 cluster in contact with the Ag(100) electrode is larger than that in the case of the Ag(110) electrode for most of investigated contact distances. With the bias voltage applied, our results also elucidate that there also exists a close correlation between the nonequilibrium properties of this cluster and the band matching between left and right electrodes in these two cases.