Embedded Green-function calculation of the conductance of oxygen-incorporated Au and Ag monatomic wires

We investigate the electronic structure and ballistic conductance of O-incorporated noble-metal atomic wires by a first-principles calculation using the embedded Green-function technique and the full-potential linearized augmented plane wave method. We consider straight monatomic wires with a single O atom inserted between two metal atoms. It will be shown that the conductance of the Au 6s (Ag 5s) channel is reduced significantly by electron scattering via the inserted O atom. On the other hand, the O 2p_x,y (π) states, which form a resonant peak near the Fermi level E_F, provide two additional conduction channels in a narrow energy range corresponding to the resonant peak. Since the d_xz,yz components of neighboring metal atoms, which hybridize with the O 2p_x,y orbitals and mediate coupling between them and the energy continuum in the leads, decay exponentially with distance from the O atom, the width of the resonance as well as the conductance associated with these two states decreases with increasing wire length. For longer wires, the wire undergoes a transition to a spin-polarized state with the O 2p_x,y resonance splitting into a fully occupied majority-spin peak and a partially occupied minority-spin peak. The latter contributes to a partially spin-polarized conductance at E_F.