First-principles study on the relaxed structures and electronic properties of Cu [110] nanowires

Under the generalized gradient approximation (GGA), first-principles calculations are employed to study the structural stability of Cu nanowires (NWs) along the [110] direction by using the projector-augmented wave potential based on the density functional theory. With the first three diameters, we present different geometrical structures of Cu [110] NWs, formed by stacking of atomic polygons with rectangular or hexagonal cross sections perpendicular to the wire axis. For all sixsized NWs, the relaxed structures still have C2 symmetry and show a “round corner” phenomenon. The calculated binding energies and electronic band structures show that the hexagonal wire is not only more stable but also more metallic than the corresponding rectangular one. Therefore, the [110]-oriented Cu NWs are energetically more likely to have hexagonal cross sections perpendicular to the wire axis, in agreement with the experimental result. The vanishing of the neighbor atoms outside the NWs after being cleaved from the bulk crystal causes the “skin effect” phenomenon. In fact, the conclusions drawn here are applicable to not only NWs but also other surfaces, such as those of nanobelts, nanotubes, nanocables, clusters, thin films, and so on.