Nanotube bundles and tube-tube orientation: A van der Waals Density Functional Study

TL;DR

This study uses van der Waals density functional theory to analyze how tube orientation affects the binding energy, electronic structure, and intertube distances in single-walled carbon nanotube bundles with various chiralities.

Contribution

It provides detailed insights into the influence of tube orientation and symmetry on the properties of nanotube bundles, highlighting the importance of relative tube orientation.

Findings

Orientation affects electronic properties and intertube distances.

Bundles with C6 symmetry exhibit metallic behavior.

Binding energies range from 19 to 35 meV/atom.

Abstract

We study the binding energy, intertube distance and electronic structure of bundles consisting of single walled carbon nanotubes of the same chirality. We model various nanotube structures (chiralities) and orientations with van der Waals density functional theory. The orientation of the tubes in the bundle strongly influences the properties of the bundles if the chirality of the tubes shares symmetry with the trigonal bundle structure, meaning chiralities which have a $60^\circ$-rotational symmetry (C$_6$-axis), e.g. ($12,0$) bundles. The bundle structure breaks the symmetry depending on the arrangement of the neighboring tubes. Pseudogaps open in the electronic density of states and intertube distances ($\pm5$-10%) vary in dependence of the relative orientation of the tubes in the bundle. Bundles of C$_6$-axis armchair tubes have metallic configurations. A $15^\circ$ rotation off the high symmetry configuration (AA-stacked) of a ($6,6$) bundle shows metallic behavior and has higher binding energy than the high symmetry configuration. We find binding energies between $19 meV/atom$ and $35 meV/atom$, depending on the chirality of the tubes. The intertube distances are between $3.2 {\AA}$ and $3.4 {\AA}$ but independent of orientation for non C$_6$-axis tubes.