First-principles calculations on boron-nitride nanotubes

Electronic and geometrical aspects of the boron-nitride nanotubes are investigated using the first-principles pseudopotential calculations. Decompositions into atomic orbitals show that overall band structures of the ideal boron-nitride nanotubes are derived from the hybridized sp(2) orbitals of boron atoms and s and p orbitals of nitrogen atoms. The incorporation of the even-membered ring in the cap of the nanotube induce a substantial hybridization between sigma and pi states of boron atoms, which leads to a significant reduction of the band gap. Several geometrical features of the boron-nitride nanotubes are described based on the revealed electronic structure.