Exchange parameters in Fe-based molecular magnets

The calculation of interatomic magnetic exchange interactions entering the Heisenberg model is outlined from the standpoint of the density functional theory (DFT) for two Fe-based molecular magnets: a trinuclear complex with a Schiff base ligand, which is an antiferromagnetically coupled frustrated system, and a model bipyrimidine-connected planar network of Fe ions. First-principles electronic structure calculations are performed using the real-space method Siesta and the full-potential linearized augmented plane wave FLAPW method FLEUR, correspondingly. We discuss the application of fixed spin moment technique for preparing the system in a given magnetic configuration, and the effect of intraatomic Coulomb correlation, approximated by the LDA + U technique, on the values of interaction parameters.