Aqueous solvation of alkaline earth metal ions plays an important role in biological and environmental processes. The water molecules most tightly bound to the cation constitute the first solvation shell. The size and flexibility of the first solvation shell affects the physical and chemical behavior of these ions. In general, the size and flexibility of the first solvation shell increases as the cation radius increases. However, the literature values for the number of water molecules within the first solvation shells of Ca2+, Sr2+, and Ba2+can vary widely based on the method used. Physically, both short-range quantum mechanical interactions and long-range electrostatic interactions are expected to contribute to the aqueous solvation of alkaline earth metal ions. A promising computational approach that includes both of these interactions is to explicitly model the first solvation shell with quantum mechanics and treat the bulk solution as a dielectric continuum. There are many computational aspects that may affect the reliability of this combined solvent model. We use density functional theory to explicitly model the alkaline earth metal ion and its first solvation shell. This quantum mechanical system is then embedded in a continuum defined by the dielectric constant of bulk water. Several computational aspects are investigated: basis set size, effective core potential, empirical dispersion model, continuum solvent model, and the continuum cavity shape. Each alkaline earth metal ion is modeled with an increasing number of explicit water molecules and results are compared with experimental coordination numbers.

Aqueous solvation of alkaline earth metal ions using combined explicit and continuum solvent

2019 Spring National Meeting

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