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 ε ∥ to grow nearly linearly with the length L and to show little dependence on the band gap. In contrast, the perpendicular screening constant ε ⊥ is strongly related to the band gap and converges for L > 10 R (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.