Endohedral Carbon Chains in Single-Wall Carbon Nanotubes

Using a first-principles, local-density-functional approach, we report the bond length optimization of endohedral linear carbon chains. In these calculations, all-carbon nanowire structures were constructed by inserting cumulenic linear carbon chains inside the semiconducting (7,3) and metallic (7,4) single-wall carbon nanotubes with radii of about 0.35 nm. Our calculations show that the total energy results for the endohedral chains inside both (7,3) and (7,4) nanotubes are well-described with a common total energy curve with an equilibrium bond length of about 0.129 nm. The electronic band structures of the carbon nanowires are described in terms of a rigidband model, with the Fermi level for the carbon nanowire effectively pinned near the top of bands originating from the valence band of the single-wall nanotube.