Ab Initio Molecular Dynamics Study of a Highly Concentrated LiCl Aqueous Solution

Abstract

The properties of a highly concentrated aqueous lithium chloride solution (|LiCl| = 14 mol L(-1)) are investigated using Car-Parrinello molecular dynamics. The coordination spheres of lithium ions, chloride ions, and water molecules are described successively. On the whole, our simulation provides results-distances and coordination numbers-in very good agreement with experimental data. The lithium solvation shell is found to exhibit a tetrahedral configuration on average, with three stable clusters observed during the simulation: Li(+)-4H2O, Li(+)(H2O)3Cl(-), and Li(+)(H2O)2(Cl(-))2. The chloride coordination sphere is logically formed by strong Cl-H hydrogen bonds with neighboring water molecules, for a mean coordination number of 4.4. The structuring of water molecules is strongly affected by the high concentration in LiCl. The hydrogen bond network is globally broken down, but little variation is calculated on water dipoles (μ = 3.07 D) because of the strong polarization from Li(+) and Cl(-) ions. We also point out some of the characteristic features of such a highly concentrated solution: water bridging between Li(+) and Cl(-) hydration spheres, Li(+)-Cl(-) ion-pairing, and intermediate behavior between dilute solutions and molten salts. Finally, the reliability of our simulation to describe ion-pairing is discussed.