Charge optimized many-body potential for iron/iron-fluoride system
A classical interatomic potential for the iron/iron-fluoride system is developed in the framework of the charge optimized many-body (COMB) potential. This interatomic potential takes into consideration the effects of charge transfer and many-body interactions depending on the chemical environment. The potential is fit to a training set composed of both experimental and ab-initio results of cohesive energies of several Fe and FeF2 crystal phases, the two fluorine molecules F2 and F2-1 dissociation energy curve, Fe and FeF2 lattice parameters of the ground state crystalline phase, and the elastic constants of the body center cubic Fe structure. The potential is tested in an NVT ensemble for different initial structural configurations as the crystal ground state phases, F2 molecules, iron clusters, and iron nanospheres. In particular, we model the FeF2/Fe bilayer and multilayer interfaces, as well as a system of square FeF2 nanowires immersed in an iron solid. It is showed that there exists a reordering of the atomic positions for F and Fe atoms at the interface zone; this rearrangement leads to an increase in the charge transfer among of the atoms that make the interface and put forward a possible mechanism to the exchange bias origin based in an asymmetric electric charge transfer in the different spin channels.