DFT-Based Polarizable Ion Models for Molten Rare-Earth Chlorides: From Lanthanum to Europium.

We developed a systematic polarizable force field for molten trivalent rare-earth chlorides, from lanthanum to europium, based on first-principle calculations. The proposed model was employed to investigate the local structure and physicochemical properties of pure molten salts and their mixtures with sodium chloride. We computed densities, heat capacities, surface tensions, viscosities, and diffusion coefficients and disclosed their evolution along the lanthanide series, filling the gaps for poorly studied elements, such as promethium and europium. The analysis of the local arrangement of chloride anions around lanthanide cations revealed broad coordination number distributions with a typical [from 6 to 9]-fold environment, the maximum of which shifts toward lower values with the increase of atomic number as well as upon dilution of the salt in sodium chloride. The neighboring lanthanide chloride complexes were found to be connected by sharing a corner or an edge of the corresponding polyhedra.