First-principles study of the stability and electronic properties of sheets and nanotubes of elemental boron

The structural and electronic properties of sheets and nanotubes of boron are investigated using density functional theory. The calculations predict the stability of a novel reconstructed {1 2 2 1} sheet over the 'idealized' triangular {1 2 1 2} sheet. Nanotubes formed by wrapping the half-metallic {1 2 2 1} sheet show a curvature-induced transition in their electronic properties. Analysis of the charge density reveals a mixed metallic- and covalent-type of bonding in the reconstructed {1 2 2 1} sheet and the corresponding nanotubes, in contrast to metallic-type bonding in the idealized {1 2 1 2} sheet and its analogous nanotubes.