Interatomic potentials consistent with thermodynamics: the cases of FeCu and FeCr

A desirable property of potentials for atomistic simulations of microstructure evolution of irradiated alloys is consistency with the experimental phase diagram. A methodology to fit semi-empirical potentials aiming at the above, recently developed by the authors, is reviewed. It is based on the coupling of the Cluster Variation Method technique --a known mean field theory for solid phase diagram computation-- to other more standard requirements, such as compliance with the energetics of some crystal structures, point-defects, etc. The method is applied to the construction of EAM many-body potentials for the FeCu system, a prototype alloy for reactor pressure vessel steels. Coherence with ab-initio computed formation energies of small point-defect clusters as well as vacancy migration energies close to Cu atoms, are incorporated. The potential is shown to match very reasonably the Cu solubility in Fe vs. temperature and obtains enhanced point-defect kinetics behavior with respect to previous potentials. Current efforts to apply the methodology to the more challenging FeCr system are also described. Here, ab-initio calculations predict slightly negative mixing enthalpies for the random alloys of low Cr content. This entails extensions of the pure EAM interaction scheme to allow for ordering effects at those Cr concentrations.