(376bh) Oxidation State of Solutes in Molten Salts from Ab Initio Molecular Dynamics Simulations

Many electrochemical processes and applications use knowledge of an ion's oxidation state. For example, for very high-temperature molten salts, experimental determination of these oxidation states is costly, therefore an ab initio molecular dynamics simulation would be preferable. However, oxidation state is not a physical observable, has no quantum mechanical operator, and cannot be determined directly from AIMD simulations. We discuss a new method to identify the oxidation state of molten salt constituents using radial distribution functions of ab initio molecular dynamics simulations. While the oxidation states of akalis and halides in ionic liquids are typically intuitive, larger ions such as transition metals are much less so. This method is applied to ions using s,p,d, and f orbitals, and the accuracy of the results are discussed, and compared with existing methods and approximations such as an extensive analysis of molecular orbital and the Bader charge distribution analysis. The flexibility of this method for liquid phases was a major motivation for its development. Potential limitations of this method, such as solvent composition or solute concentration, are also discussed.