Bundle and chirality influences on properties of carbon nanotubes studied with van der Waals density functional theory

Abstract We study the binding strength and intertube distance of carbon nanotube bundles in dependence of their structure (chirality) with van der Waals density functional theory. We try to understand the bundling and debundling process of nanotube bundles and test whether an influence of chirality exists. The distance between the nanotubes in the bundles vary only in a small range within 3.3 and 3.4 Å, without any chiral angle and diameter dependence. We find an increase of van der Waals energy per length with increasing diameter of the nanotubes ${\left( {E_{{\rm vdW}}^{{\rm length}} {\propto} d\,{\rm or}\,\sqrt {d} } \right)}$ for tubes with diameters between 5.6 and 27.3 Å, but no obvious correlation between the chirality of the tubes and the van der Waals energy per length. The van der Waals energy per atom is decreasing with increasing tube diameter ${\left( {E_{{\rm vdW}}^{{\rm atom}} {\propto} 1/d\,{\rm or}\,1/\sqrt {d} } \right)}$ .