Ab initio calculations on the open end of single-walled BN nanotubes

Geometrical and electronic structures of open-ended armchair and zigzag single-walled boron nitride (BN) nanotubes are calculated using density functional theory with the generalized gradient approximation. The BN dimers at the open end of armchair BN nanotubes are buckled greatly, i.e., B atoms move inward and N atoms move outward, on which the size of BN nanotubes has a very small influence. The ionization potential of the B-terminated zigzag BN nanotube is smaller than that of the N-terminated BN nanotube due to the opposite direction of the surface dipole moment, which makes a B-terminated zigzag BN nanotube more efficient for field electron emission than the corresponding N-terminated BN nanotubes.