Structure and dynamics of water on aqueous barium ion and the {001} barite surface

The structure of water and its dynamics affect a number of fundamental properties of an interface. Yet, these properties are often inaccessible experimentally and computational studies including solvent are comparatively few. Here, we estimate the structure and kinetics of water exchange of aqueous barium ions and barium ions within the {001} barite surface using molecular dynamics and the reactive flux method. For the aqueous ion, the Ba-O distance to water in the first hydration shell was found to be 280 pm with a coordination number of 8.3, and the best estimate of the exchange rate constant is 4.8 × 10 ⁹ s ^-1, closely matching experimental estimates. For the barite surface, the first shell water distance was 282 pm, with a coordination number of 0.9 and the best estimate of the rate constant for exchange is 1.7 × 10 ¹⁰ s ^-1, 3.5 times faster than that of the aqueous ion.