Microscopic polarization in ropes and films of aligned carbon nanotubes

The microscopic electric polarization in terms of the dipole-dipole polarizability and its second hyperpolarizability of aligned films and ropes of carbon nanotubes has been studied theoretically by a point-dipole interaction model. The results show clearly the influence of intertube interactions on the microscopic polarization demonstrating the sensitivity of the electronic structure of carbon nanotubes to the surroundings. Both the polarizability and the second hyperpolarizability are screened due to the intertube interactions and deviate substantially from an additive model. It is noted that both the polarizability and the second hyperpolarizability reach their minimum values around the van der Waals separation. In the rope arrangement the polarizability of a tube is reduced by 10% and the second hyperpolarizability by as much as 50% as compared to an unperturbed tube.