Non-local correlation effects due to virtual spin-flip processes in itinerant electron ferromagnets

We present an ab initio method for eletcronic structure calculations, which accounts for the interaction of electrons and magnons in ferromagnets. While it is based on a many body perturbation theory we approximate numerically complex quantities with quantities from time dependent density functional theory. This results in a simple and affordable algorithm which allows us to consider more complex materials than those usually studied in this context ($3d$ ferromagnets) while still being able to account for the non-locality of the self energy. Furthermore, our approach allows for a relatively simple way to incorporate self-consistency. Our results are in a good agreement with experimental and theoretical findings for iron and nickel. Especially the experimental exchange splitting of nickel is predicted accurately within our theory. Additionally, we study the halfmetallic ferromagnet NiMnSb concerning its non-qusiparticle states appearing in the bandgap due to spin-flip excitations.