Molecular dynamics study of phonon transport in graphyne nanotubes

We determine the thermal conductivities of a, b, and g graphyne nanotubes (GNTs) as well as of carbon
nanotubes (CNTs) using molecular dynamics simulations and the Green-Kubo relationship over the
temperature range 50e400 K. We find that GNTs demonstrate considerably lower thermal conductivity
than CNTs with the same diameter and length. Among a (alpha), b (beta), and g (gama)-GNTs, g-GNT has the highest thermal
conductivity at all temperatures. By comparing the phonon transport properties of GNTs with CNTs, we
find that as the fraction of acetylene bonds in the atomic network increases, the population of highenergy
optical phonons increases. This enhances phonon-phonon scattering, and reduces the mean
free path, adversely affecting the thermal conductivity of GNTs relative to CNTs. Also reducing the
thermal conductivity of GNTs relative to CNTs is the considerably lower acoustic phonon group velocities
for the former as well as the lower volumetric heat capacity of GNTs. Optical phonons in a-GNT are high
in energy (0.26 eV) with a high population number, making them more energetic than the electronic
direct band gap and significantly more energetic than the thermal energy at room temperature.
Therefore, we suggest a-GNT as a potential candidate for phonovoltaic energy conversion applications.