Strength of effective Coulomb interactions in graphene and graphite
  To obtain an effective many-body model of graphene and related materials from first principles we calculate the partially screened frequency dependent Coulomb interaction. In graphene, the effective on-site (Hubbard) interaction is U_00 = 9.3 eV in close vicinity to the critical value separating conducting graphene from an insulating phase emphasizing the importance of non-local Coulomb terms. The nearest-neighbor Coulomb interaction strength is computed to U_01 = 5.5 eV. In the long wavelength limit, we find the effective background dielectric constant of graphite to be \epsilon = 2.5 in very good agreement with experiment. 
T. O. Wehling, E. Sasioglu, C. Friedrich, A. I. Lichtenstein, M. I.   Katsnelson, and S. Bl\"ugel
cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.str-el