Screened Coulomb interaction of localized electrons in solids from first principles

We report the implementation of a first-principles approach for calculating the screened Coulomb and exchange energies for localized electrons in solids. Our method is based on the pseudopotential plane-wave formalism. The localized orbitals are represented by maximally localized Wannier functions, and the screening effects are calculated within the constrained random phase approximation. As first applications of this development, we investigate the onsite Coulomb U and exchange J for the 3d electrons in ZnO, NiO, and CuGaS2. Both the bare (unscreened) and the screened U and J matrices are presented. We find that it is very important for these parameters to be calculated self-consistently. Intrachannel (i.e., d-d) and energy-dependent screening effects are also discussed.