Molecular Dynamics Study of the Coordination Sphere of Trivalent Lanthanum in a Highly Concentrated LiCl Aqueous Solution: a Combined Classical and Ab Initio Approach

The first coordination sphere of trivalent lanthanum in a highly concentrated (14 M) lithium chloride solution is studied with a combination of classical molecular dynamics and density functional theory based first principle molecular dynamics. This method enables us to obtain a solvation shell of La3+ containing 2 chloride ions and 6 water molecules. After refinement using first principle molecular dynamics, the resulting cation-water and cation-anion distances are in very good agreement with experiment. The 2Cl- and the 6 water molecules arrange in a square antiprism around La3+. Exchange of water molecules was also observed in the first-principle simulation, with an intermediate structure comprising 7 water molecules stable for 2.5 ps. Finally, evaluation of dipole moments using maximally localized Wannier functions shows a substantial polarization of the choride anions and the water molecules in the first solvation shell of trivalent lanthanum.