Frequency-dependent local interactions and low-energy effective models from electronic structure calculations

We propose a systematic procedure for constructing effective models of strongly correlated materials. The parameters, in particular the on-site screened Coulomb interaction $U$, are calculated from first principles, using the random-phase approximation. We derive an expression for the frequency-dependent $U(\ensuremath{\omega})$ and show, for the case of nickel, that its high-frequency part has significant influence on the spectral functions. We propose a scheme for taking into account the energy dependence of $U(\ensuremath{\omega})$, so that a model with an energy-independent local interaction can still be used for low-energy properties.