Density functional calculations are used to predict the electronic structur
es of GaN nanotubes. The graphitic GaN is an indirect band gap material wit
h valence band maximum at K edge. Zigzag nanotube is a semiconductor with d
irect band gap, whereas armchair nanotube has an indirect band gap along th
e tube axis. The band gaps decrease with the decreasing diameter, contrary
to the case of carbon nanotubes.