  The configurations, stability and electronic structures of a new class of
boron sheet and related boron nanotubes are predicted within the framework of
density functional theory. This boron sheet is sparser than those of recent
proposals. Our theoretic results show that the stable boron sheet remains flat
and is metallic. There are bands similar to the p-bands in graphite near the
Fermi level. Stable nanotubes with various diameters and chiral vectors can be
rolled from the sheet. Within our study, only the thin (8, 0) nanotube with a
band gap of 0.44 eV is semiconducting, while all the other thicker boron
nanotubes are metallic, independent of their chirality. It indicates the
possibility, in the design of nanodevices, to control the electronic transport
properties of the boron nanotube through the diameter.
