The DFT+$\Sigma_2$ method for electron correlation effects at transition metal surfaces.

We present a computational approach for electronically correlated metallic surfaces and interfaces, which combines Density Functional and Dynamical Mean Field Theory using a multi-orbital perturbative solver for the many-body problem. The performances are assessed in detail for a Fe monolayer on a W(110) substrate, a prototypical nanoscale magnetic system. We find qualitative and quantitative improvements in the calculated spectral function compared to the results of density functional theory within the local spin density approximation. In particular, the spin-splitting of the $d$ states is drastically reduced and, at the same time, their spectral width becomes narrower. Additionally, the method predicts the appearance of satellites, genuine many-body effects, at higher binding energies.