▎ 摘　　要

We determine, by means of density-functional theory, the stability and the structure of graphene-nanoribbon (GNR) edges in presence of molecules such as oxygen, water, ammonia, and carbon dioxide. As in the case of hydrogen-terminated nanoribbons, we find that the most stable armchair and zigzag configurations are characterized by a nonmetallic/nonmagnetic nature, and are compatible with Clar's sextet rules, well known in organic chemistry. In particular, we predict that, at thermodynamic equilibrium, neutral GNRs in oxygen-rich atmosphere should preferentially be along the armchair direction while water-saturated GNRs should present zigzag edges. Our results promise to be particularly useful to GNRs synthesis since the most recent and advanced experimental routes are most effective in water and/or ammonia-containing solutions.