Structure of boron nitride nanotubes: tube closing versus chirality

The structure of boron nitride nanotubes is investigated using a generalized tight-binding molecular dynamics method. It is shown that dynamic relaxation results in a wave-like or `rippledʹ surface in which the B atoms rotate inward and the N atoms move outward, reminiscent of the surface relaxation of the III–V semiconductors. More importantly, the three different morphologies of the tube closing with flat, conical and amorphous ends, as observed in experiments, are shown to be directly related to the tube chiralities.