▎ 摘　　要

We discuss low-energy electronic properties of distorted graphene sheets from a local geometric viewpoint, treating curvature and strain as perturbations of a smooth surface. This allows a unified description of the variety of deformations to which carbon nanotubes are susceptible. By using a general symmetry analysis in conjunction with a four-orbital, nonorthogonal tight-binding model, we calculate accurate values of the relevant couplings.