▎ 摘　　要

Experimentally measured electronic band gaps of atomically sharp straight and chevronlike armchair graphene nanoribbons (GNRs) adsorbed on a gold substrate are smaller than theoretically predicted quasiparticle band gaps of their free-standing counterparts [Linden et al., Phys. Rev. Lett. 108, 216801 (2012)]. The influence of the substrate on electronic properties of both straight and chevronlike GNRs is here investigated including many-body effects beyond semilocal density-functional theory. The predicted small electron transfer from a straight or chevronlike GNR to the gold surface is found to lead to a surface polarization at the GNR-metal interface responsible for a significant reduction of the quasiparticle band gap of the GNR. This reduction is quantified using a semiclassical image charge model. By considering both quasiparticle and surface polarization corrections, we obtain theoretical band gaps that are consistent with experimental ones for gold-supported GNRs.