First Principles Molecular Dynamics Investigation of Bulk and Interfacial Aqueous Fluoride

Using first principles molecular dynamics simulation, we have embedded a fluoride anion into a water slab composed of 215 water molecules to mimic bulk and interfacial solvation. Our findings indicate that there are small structural changes for fluoride and its first solvation shell but the presence of fluoride does not alter the rotational dynamics of nearby water. In addition, we have computed the molecular dipole moments using Wannier centers. At the interface, the presence of fluoride increases the molecular dipole moments of nearby water molecule, whereas in the bulk the molecular dipole moments for water appears to be invariant to the presence of fluoride in the vicinity. Previous study of the air-water interface shows water at the interface have higher average HOMO energies and thus more prone to electrophilic attack. With the addition of fluoride, the most likely reactive site for electrophilic reactions shifts to the anion. This could explain the large increase in reaction rates for heterogeneous process. The reactive properties of other anions near the GDS are of great interest in heterogeneous chemistry and can be elucidated using the same type of analysis performed here for fluoride anion