  Using density functional theory, we study physical properties of boron
nitride nanotubes (BNNTs) with the substitutional carbon pair defect. We also
consider the Stone-Wales (SW) rearrangement of the C-C pair defect in the BNNT.
The formation energy of an SW defect of the carbon dimer is approximately 3.1
eV lower than that of the SW-transformed B-N pair in the undoped BNNT. The
activation energies show that the SW defect in the C-doped BNNT may be
experimentally observed with a higher probability than in the undoped BNNT.
Finally, we discuss the localized states originating from the carbon pair
impurities.
