Frequency-dependent polarizability of boron nitride nanotubes: A theoretical study

In the present work, we have calculated the static and frequency-dependent polarizability tensors for a series of single-walled boron nitride nanotubes and compared them with corresponding results for carbon nanotubes. The calculations have been performed by employing a dipole-dipole interaction model based on classical electrostatics and an Unsold dispersion formula. In comparison, we have carried out ab intio calculations at the SCF level of the static polarizability of the smaller nanotubes with the STO-3G basis set. For the frequency-dependent polarizability Of C-60, we found excellent agreement among the most accurate SCF calculations in the literature, the interaction model, and experimental results. In particular, the frequency dependence is modeled accurately indicating that the interaction model is a useful tool for studying the frequency dependence of materials. For the nanotubes, we observe the same trends in the interaction model and in the SCF STO-3G results when the number of atoms is increased. However, the values obtained with the interaction model are about 100% larger than the corresponding SCF STO-3G results, due to the small size of the STO-3G basis set. We also find that the boron nitride nanotubes have smaller magnitudes of the polarizability tensor components than the corresponding components for the carbon nanotubes with the same geometry and number of atoms. Furthermore, we find that the geometry of the tube has a large influence on the anisotropy of the polarizability components, whereas the mean polarizability remains almost unaffected when the geometrical configuration is modified. Finally, we observe a relatively small frequency dependence of the polarizability tensor of BN nanotubes.