The thermoelectric transport through carbon chains

We investigate the thermoelectric transport properties of carbon atomic clusters connected with two Al electrodes using the first-principles density functional analysis combined with the non-equilibrium Green's function approach. We find that due to the quantum interference the thermopower S changes sign for even-odd number of carbon atoms. The thermal conductance κ is always positive with a similar oscillation between even- and odd-number of carbon atoms. Due to the orthogonalization of the wave functions of the atomic electrodes and the carbon clusters, the electric conductance G is very small for certain range of chemical potentials. Giant thermopower is found in this region. Our results show that the thermopower and thermal conductance are sensitively related to the distance d between the carbon atomic cluster and the Al electrodes. Oscillatory behaviors of S and κ are found as d is varied.