Finite-size effect and wall polarization in a carbon nanotube channel

The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied in view of their technical applications. For this purpose, a self-consistent tight-binding method, which captures the periodic oscillation pattern of the finite band gap as a function of tube length, is applied. We find the parallel screening constant epsilon(parallel to) to grow nearly linearly with the length L and to show little dependence on the band gap. In contrast, the perpendicular screening constant epsilon(perpendicular to) is strongly related to the band gap and converges for L > 10R (radius) to its bulk value. Our description is employed to study the wall polarization in a short (6,6) nanotube filled with six water molecules, a situation that arises with technical uses of carbon nanotubes as channels.