Curvature effects on electronic properties of armchair graphene nanoribbons without passivation

The geometric and electronic properties of curved armchair graphene nanoribbons without hydrogen atoms are investigated by first-principles calculations. The edge-atom bond length and ground state energy dramatically vary with the arc angle. The zipping or unzipping requirements for energy, arc angle, and interaction distance depend on the ribbon width. The increasing curvatures lead to drastic changes in electronic structures, such as energy gaps, energy dispersions, band-edge states, band mixing, band overlap and state degeneracy. There exist semiconductor-metal transitions during the variation of curvature. These are associated with the contribution of the edge atoms, the competition between the π and σ bonds, and hybridization of the 2p _y and 2p _z orbitals. The main features of the energy bands dominate the frequency, height, number, and structure of the prominent peaks in the density of states. The predicted results could be examined by experimental measurements.