Static and optical transverse and longitudinal screened polarizabilities of boron nitride nanotubes

We have investigated static and optical transverse and longitudinal screened polarizabilitics of single-walled (SWBNNT) and multiwalled (MWBNNT) boron nitride nanotubes by using the density functional perturbation theory. The static and optical transverse and longitudinal screened polarizabilities of SWBNNTs all increase linearly with the radius and are smaller than those of similar-sized single-walled carbon nanotubes. The screened optical transverse polarizabilities of SWBNNTs are found to be about half that of the unscreened ones. In addition to the screened polarizabilities themselves, the ratio between the static and optical screened polarizabilities of SWBNNTs also exhibits anisotropy. In contrast to multiwalled carbon nanotubes, where the inner tube is almost completely shielded by the outer tube, in MWBNNTs, the inner tube is only partially shielded by the outer tube when a transverse electric field is applied.