The existence of stable layered bulk allotropes can be an indication for the existence of corresponding stable tubular structures. Using a density functional tight binding method we demonstrate that charged borocarbide (BC) nanotubes, which are isoelectronic with layered lithium or copper borocarbide, are stable and energetically viable. The discussed structures are semiconducting with an energy gap which decreases with diameter. The size of the gap also depends on the helicity of the tubes, and is always smaller for tubes with armchair $\mathrm{}(n,n)\mathrm{}$ and zig-zag $\mathrm{}(3n,0)\mathrm{}$ symmetry than for tubes with other symmetries. Hole doping and its effects on the electronic structure of ${\mathrm{BC}}^{\left(-\right)}$ layers and tubes is also discussed.

• Received 16 September 2002

DOI:https://doi.org/10.1103/PhysRevB.67.125401