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<p>As natural aqueous solutions are far from
being pure water, being rich in ions, the properties of solvated ions are of
relevance for a wide range of systems, including biological and geochemical
environments. We conducted ab initio and classical MD simulations of the
alkaline earth metal ions Mg<sup>2+</sup> and Ca<sup>2+</sup> and of the alkali
metal ions Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup> and Cs<sup>+</sup> in
pure water and electrolyte solutions containing the counterions Cl<sup>–</sup>
and SO<sub>4</sub><sup>2–</sup>. Through a detailed analysis of these
simulations, this study reports on the effect of solution chemistry
(composition and concentration of the solution) to the ion–water structural
properties and interaction strength, and to the dynamics, hydrogen bond
network, and low-frequency dynamics of the ionic solvation shell. Except for
the ion–water radial distribution function, which is weakly dependent on the
counter-ions and concentrations, we found that all other properties can be
significantly influenced by the chemical characteristics of the solution.
Calculation of the velocity autocorrelation function of magnesium ions, for
example, shows that chlorine ions located in the second coordination shell of
Mg<sup>2+</sup> weaken the Mg(H<sub>2</sub>O)<sub>6</sub><sup>2+</sup>
hydration ‘cage’ of the cation. The result reported in this study suggest that
ionic solvation shell can be significantly influenced by the interactions
between other ions present in solution ions, especially those of opposite
charge. In more general terms, the chemical characteristics of the solution,
including the balance between ion-solvent and ion-ion interactions, could
result in significant differences in behavior and function of the ionic
solvation shell.</p>
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Impact of Solution Chemistry and Particle Anisotropy on the Collective Dynamics of Oriented Aggregation
