The edge states and optical transition energies in carbon nanoribbons are investigated with density-functional calculations. While the ground state of zigzag ribbons is spin polarized, defects at the edges destroy spin polarization and lead to a nonmagnetic ground state. Scanning tunneling spectroscopy will thus show different features depending on edge quality. Optical transition energies in nanoribbons $E_{ii}$ are strongly affected by the edges and confinement, which introduce a term inversely proportional to their width. After removing that term, the scaling of $E_{ii}$ is quantitatively similar to that in carbon nanotubes.

• Received 12 June 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.246803