First-principles study of narrow single-walled GaN nanotubes

Structural and electronic properties of narrow single-walled GaN nanotubes with diameter from 0.30 to 0.55 nm are investigated using the density functional method with generalized-gradient approximation. The calculations of total energies predict that the most likely GaN nanotubes in our calculation are (2,2), (3,2) and (3,3) nanotubes. From a detailed analysis we find that these narrow single-walled GaN nanotubes are all semiconductors, of which the armchair and chiral tubes are indirect-band-gap semiconductors whereas the zigzag ones have a direct gap except for (4, 0) tube. The indirect band gap of (4, 0) tube can stem from band sequence change induced by curvature effect. Our results show that the pi-pi hybridization effect and the formation of benign buckling separations play a key role in the band sequence changes of (4, 0) tube. (C) 2008 Elsevier B.V. All rights reserved.