Ab initio molecular dynamics calculations have been used to study the dynamical properties of the strontium
hydration shell as a function of temperature. At 25 °C, we obtained Sr−O bond lengths of 2.6 Å and a
coordination number of 7.5. These are in good agreement with available experimental data. Increasing the
temperature to 350 °C led to a decrease in the coordination number to 6.7 and a contraction of the first shell
by about 0.1 Å. This is in agreement with the data which predict octahedral coordination of Sr in water at
high temperatures. Our calculated Debye−Waller factors also agree well with the experimental values. At
higher temperatures (600 °C), we predict that the Sr ion remains in 6-fold coordination.
We determined the coordination environment of Zn 2+ in aqueous Clbrines at 25 °C and 300 °C using ab initio molecular dynamics simulations. The ZnCl + and ZnCl 2 complexes exist as pseudo-octahedral ZnCl m (H 2 O) 6-m clusters at 25 °C but occur as pseudo-tetrahedral ZnCl m (H 2 O) 4-m clusters at 300 °C. The ZnCl 3complex occurs as the pseudo-tetrahedral ZnCl 3 (H 2 O)cluster at 25 and 300 °C. The tetrahedral ZnCl 4 2complex, however, is the dominant Zn-Cl complex at 25 °C, at least in highly concentrated (7.4 m) Clbrines. The change in hydration number with temperature for the ZnCl + and ZnCl 2 complexes will complicate extrapolations of solvation energies to hydrothermal conditions using a Born-model-based equation of state.
We have modelled the surface diffusion and growth of BaO and SrO both in the homoepitaxial and heteroepitaxial (BaO on SrO and SrO on BaO) cases. The diffusion proceeds most favourably by an exchange mechanism involving the surface layer. When impurities are adsorbed on the surface this can lead to intermixing between the layers. This strongly suggests that ionic materials may not be grown on a substrate with a similar structure without significant intermixing. Island growth begins with the formation of individual clusters which grow and merge together.
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