Transport through a single-atom junction

We have performed first-principles density functional calculations in conjunction with a three-dimensional evaluation of the quantum scattering matrix for single-atom Si and Al tunnel junctions. We predict the equilibrium conductance and resonance transmission properties. Our results unambiguously show that when the atom is somewhat isolated from the electrodes, the differential electric current should show resonances due to atomic valence orbitals. The conductance resonance peaks may or may not retain a universal value, depending on whether or not there is a partial overlap of the resonance transmissions. Our results also clearly demonstrate the formation of a wire when the atomic junction becomes less and less isolated from the electrodes.