Finite-Size Effect and Wall Polarization in a Carbon Nanotube Channel

Abstract

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 E | to grow nearly linearly with the length L and to show little dependence on the band gap. In contrast, the perpendicular screening constant E ⊥ 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.

Transport phenomena in nanofluidics

“…At such length scales, molecular-dynamics simulations are used to determine transport in nanopores for a specific period of time with known physical laws ͑Qiao and Aluru, 2003Lu et al, 2004͒. In a typical molecular-dynamics simulation, a set of molecules with initial random positions is assumed, to which are assigned initial random velocities corresponding to the Boltzmann distribution at the temperature of interest.…”

Screening of water dipoles inside finite-length armchair carbon nanotubes

“…The dielectric behavior is studied by turning on a uniform electric field along the nanotube axis and extracting resulting changes of the Mulliken atomic charges [8], from which the electrostatic potential profile and dielectric constant are calculated. Our preliminary ab initio calculation shows that the screening ability of the optimized structure is slightly decreased [9], while the main conclusions in this paper remain valid.…”

“…However, the SWNTs studied in molecular dynamics (MD) simulations are usually modeled as non-polar channels interacting with the ambient environment through a short-ranged van der Waals potential, while little attention is paid to the polarizable nature of the SWNTs. Unlike many biological channels, SWNTs are highly polarizable due to their delocalized π-electrons, which respond effectively to external electric fields [3]. algorithm to capture the polarization effect of SWNTs for realistic biological applications is thus in high demand.…”

Carbon nanotube screening effects on the water-ion channels

“…Prior studies have investigated screening effects of CNTs under uniform parallel and transverse electric fields. [7][8][9][10][11] Semiconducting CNTs demonstrated significantly weaker screening compared to metallic CNTs. Relatively less efforts have been invested to study the polarizability and screening effects of CNTs under general electric fields generated by water dipoles and charged ions inside SWCNTs.…”

“…6 Despite many successful predictions by MD simulations, the nanotube models used in existing MD simulations provide an incomplete description of nanotube electrostatics as they ignore the nanotube polarizability. 7 SWCNTs can be semiconducting or metallic depending upon the tube diameter and the chirality. 8 Among the general chiral ͑n , m͒ CNTs with infinite lengths, all armchair nanotubes and those with n − m =3j ͑j being a nonzero integer͒ are metallic.…”