Termini effects on the optical properties of graphene nanoribbons

First principles the optical response of finite-length armchair-edged graphene nanoribbons (AGNRs) within the framework of many-body perturbation theory. As a result of the explicit inclusion of zigzag extremities, we identify low-energy and low-intensity excitations that are expected to be almost independent of the GNR length. These excitations coexist with bulk-like excitations, which have the same origin as the ones characterizing infinite AGNRs. Our results are used to rationalize termini effects on the optical response of GNRs and to shed light on recent photoluminescence data.