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The conductance of carbon-atom chains is found from first-principles calculations to vary in an oscillatory manner as the number of carbon atoms is increased, with odd-numbered chains having a lower resistance than even-numbered chains. This finding is explained in terms of the electronic structure of the free chains and its modification by interaction with the metal electrodes: the critical factor is the density of states at the Fermi level of the combined electrode--atomic-wire system. Stronger electrode--atomic-wire coupling, i.e., shorter metal-carbon distance, does not necessarily imply a higher conductance.
Lang et al. (Mon,) studied this question.