 Nanotube zone folding

An approximation that samples the graphene bands on wave vectors satisfying $\mathbf{k}\cdot {\mathbf{C}}_h=2\pi \ell$, where ${\mathbf{C}}_h$ is the carbon nanotube chiral vector. It produces one-dimensional subbands and the ideal metallicity criterion $n-m\equiv 0(\mathrm{mod}3)$; curvature and interactions can modify its predictions.