  In this Letter, we put forward a resolution to the prolonged ambiguity in
energy band gaps between theory and experiments of fabricated graphene
nanoribbons (GNRs). Band structure calculations using density functional theory
are performed on oxygen passivated GNRs supercells of customized edge
configurations without disturbing the inherent sp2 hybridization of carbon
atoms. Direct band gaps are observed for both zigzag and armchair GNRs,
consistent with the experimental reports. In addition, band gap values of GNRs
scattered about an average value curve for a given crystallographic orientation
are correlated with their width on basis of the edge configurations elucidates
the band gaps in fabricated GNRs. We conclude that edge configurations of GNRs
significantly contribute to band gap formation in addition to its width for a
given crystallographic orientation, and would play a crucial role in band gap
engineering of GNRs for future research works on fabrication of nanoelectronic
devices.
