  We investigate the electronic structures of some defective boron nitride
nanotubes (BNNTs) under transverse electric fields within density-functional
theory. (16,0) BNNTs with antisite, carbon substitution, single vacancy, and
Stone-Wales 5775 defects are studied. Under transverse electric fields, the
band gaps of the defective BNNTs are reduced, similar to the pristine ones. The
energy levels of the defect states vary with the transverse electric field
directions, due to the different electrostatic potential shift at the defect
sites induced by the electric fields. Therefore, besides electronic structure
and optical property engineering, the transverse electric field can be used to
identify the defect positions in BNNTs.
