Even–odd behavior and quantization of conductance in monovalent atomic contacts

A Friedel-sum-rule-aided first-principles conductance calculation is presented for a sodium monatomic wire suspended between two bulk electrodes with sharp tip geometry. The conductance (G) is found to oscillate with the number (L) of atoms in the wire. For odd L, G has a quantized value of View the MathML source, which is robust to the variation in wire geometry, while G is smaller than G0 for even L, sensitive to the wire geometry. This even–odd behavior results from the sharp electrode tip and charge neutrality; the former generates resonant states, and the latter pins one of the resonant states at the Fermi energy for odd L.