Plasmonic and dielectric properties of ideal graphene

Graphene is a paradigm for 2D nano materials. We present electron energy loss spectra (EELS) and dielectric functions for graphene over several intervals of excitation energy and momentum transfer. We explore the difficulty of properly taking into account the vicinity of the Dirac point, which limits the resolution in the lower energy limit. For this we performed high resolution linear response time-dependent density functional theory (LRTDDFT) calculations of the dielectric function. Our results show a strong increase in the dielectric response approaching the static limit, which is linked to a Dirac-like cone, and which is not connected with plasmon resonances.