Ab InitioGWMany-Body Effects in Graphene

Abstract

We present an ab initio numerical many-body $GW$ calculation of the band plot in freestanding graphene. We consider the full ionic and electronic structure introducing $e\mathrm{\text{−}}e$ interaction and correlation effects via a self-energy containing non-Hermitian and dynamical terms. With respect to the density-functional theory local-density approximation, the Fermi velocity is renormalized with an increase of 17%, in better agreement with the experiment. Close to the Dirac point the linear dispersion is modified by the presence of a kink, as observed by angle-resolved photoemission spectroscopy. We demonstrate that the kink is due to low-energy $\pi \to {\pi }^{*}$ single-particle excitations and to the $\pi$ plasmon. The $GW$ self-energy does not open the band gap.