  Electronic properties of graphene quantum dots (GQDs) constitute a subject of
intense scientific interest. Being smaller than 20 nm, GQDs contain confined
excitons in all dimensions simultaneously. GQDs feature a non-zero band gap and
luminesce on excitation. Tuning their electronic structure is an attractive
goal with a technological promise. In this work, we apply density functional
theory to study an effect of neutral ionic clusters adsorbed on GQD surface. We
conclude that both HOMO and LUMO of GQD are very sensitive to the presence of
ions and to their distance from the GQD surface. However, the alteration of the
band gap itself is modest, as opposed to the case of free ions (recent
reports). Our work fosters progress in modulating electronic properties of
nanoscale carbonaceous materials.
