  The heat flux autocorrelation functions of carbon nanotubes (CNTs) with
different radius and lengths is calculated using equilibrium molecular
dynamics. The thermal conductance of CNTs is also calculated using the
Green-Kubo relation from the linear response theory. By pointing out the
ambiguity in the cross section definition of single wall CNTs, we use the
thermal conductance instead of conductivity in calculations and discussions. We
find that the thermal conductance of CNTs diverges with the CNT length. After
the analysis of vibrational density of states, it can be concluded that more
low frequency vibration modes exist in longer CNTs, and they effectively
contribute to the divergence of thermal conductance.
