Electronic and optical properties of ultrathin single walled boron nanotubes – An ab initio study

We have employed density functional theory calculations in generalized-gradient approximation to investigate electronic and optical properties of single walled boron nanotubes. We have calculated binding energy per atom, band structure, partial density of states, dielectric function, absorption spectra and loss function for armchair (3, 3), zigzag (5, 0) and chiral (4, 2) nanotubes. Our calculations show that (4, 2) nanotube is highly stable and semiconducting with direct band gap of 0.40 eV followed by armchair (3, 3) and zigzag (5, 0) nanotubes depicting metallic nature. The optical properties of periodic nanotubes were performed for parallel and perpendicular polarized light. It is found that all the three nanotubes are anisotropic in nature and chiral (4, 2) nanotube showing single peak for both absorption spectra as well as loss function irrespective of polarization direction.