Quantum plasmonics in graphene nano-flakes: A time-dependent density functional theory study

The optical spectra for a variety of single and coupled graphene nano-flakes have been studied using time-dependent density functional theory within generalized gradient approximation. The time evolution of the charge density induced by a continuous-wave electrical field excitation has been calculated as well, in order to investigate the plasmonic properties of these graphene nano-structures. For the small graphene nano-flakes (diameter ~1nm), the edge plasmons are dominant, whereas for larger ones (diameter ~2nm) the edge plasmons are accompanied by multipolar collective charge oscillations, a typical characteristics for surface plasmons. This study might be used to guide the experimental observation of quantum plasmons in graphene nano-structures.