Structure of boron nitride nanotubes: tube closing versus chirality

The structure of boron nitride nanotubes is investigated using a generalize d tight-binding molecular dynamics method. It is shown that dynamic relaxat ion results in a wave-like or 'rippled' 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 morphol ogies of the tube closing with flat, conical and amorphous ends, as observe d in experiments, are shown to be directly related to the tube chiralities. (C) 1999 Elsevier Science B.V. All rights reserved.