ELECTRONIC EXCITATIONS IN NANOSCALE SYSTEMS WITH HELICAL SYMMETRY

A complete set of helically symmetric wave functions is constructed an d is used to set up the Bloch-like states for describing the electroni c band structure of nanoscale systems with helical symmetry. Various h elical arrangements leading to different graphitic tubules may be obta ined by rolling the two-dimensional honeycomb lattice into a cylinder subjected to appropriate periodic boundary conditions. A discussion of the symmetries of these helices is given. This method is applied to s tudy the electronic structure of graphitic tubules and is compared wit h other methods found in the literature.