Static dielectric response and born effective charge of BN nanotubes from ab initio finite electric field calculations

Ab initio investigations of the full static dielectric response and Born effective charge of BN nanotubes (BN-NTs) have been performed using finite electric-field method. It is found that the ionic contribution to the static dielectric response of BN-NTs is substantial and also that a pronounced chirality-dependent oscillation is superimposed on the otherwise linear relation between the longitudinal electric polarizability and the tube diameter $(D)$, as for a thin dielectric cylindrical shell. In contrast, the transverse dielectric response of the BN-NTs resembles the behavior of a thin (nonideal) conducting cylindrical shell of a diameter of $D+4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, with a screening factor of 2 for the inner electric field. The medium principal component ${Z}_{y}^{*}$ of the Born effective charge, corresponding to the transverse atomic displacement tangential to the BN-NT surface, has a pronounced $D$ dependence (but independent of chirality), while the large longitudinal component ${Z}_{z}^{*}$ exhibits a clear chirality dependence (but nearly $D$ independent), suggesting a powerful way to characterize the diameter and chirality of a BN-NT.