Electronic and piezoelectric properties of BN nanotubes from hybrid density functional method

The electronic and piezoelectric properties of the boron nitride (BN) nanotubes are investigated using the hybrid density functional (B3LYP) method. The energy gap and band structure of the bulk h-BN and BN sheet by the B3LYP method are in good agreement with those by the GW method. We find that compared with the local-clensity-approximation calculations, the B3LYP calculations increase the energy gap by a almost constant (1.8 eV) for both zigzag and armchair nanotubes with various radius. We give an alternative interpretation that the optical absorption lines at 4.45 eV might be due to the electron transition in small zigzag BN nanotubes. The piezoelectric constants from the B3LYP method for zigzag BN nanotubes are substantially larger than those in the PVDF polymer family, suggesting BN nanotubes as candidates for various nanoelectromechanical applications.