A theoretical study of the structural and electronic properties of thechloride ion and water molecules in the first hydration shell is presented. Thecalculations are performed on an ensemble of configurations obtained frommolecular dynamics simulations of a single chloride ion in bulk water. Thesimulations utilize the polarizable AMOEBA force field for trajectorygeneration, and MP2-level calculations are performed to examine the electronicstructure properties of the ions and surrounding waters in the external fieldof more distant waters. The ChelpG method is employed to explore the effectivecharges and dipoles on the chloride ions and first-shell waters. The QuantumTheory of Atoms in Molecules (QTAIM) is further utilized to examine chargetransfer from the anion to surrounding water molecules. From the QTAIM analysis, 0.2 elementary charges are transferred from the ionto the first-shell water molecules. The default AMOEBA model overestimates theaverage dipole moment magnitude of the ion compared with the estimated quantummechanical value. The average magnitude of the dipole moment of the watermolecules in the first shell treated at the MP2 level, with the more distantwaters handled with an AMOEBA effective charge model, is 2.67 D. This value isclose to the AMOEBA result for first-shell waters (2.72 D) and is slightlyreduced from the bulk AMOEBA value (2.78 D). The magnitude of the dipole momentof the water molecules in the first solvation shell is most strongly affectedby the local water-water interactions and hydrogen bonds with the secondsolvation shell, rather than by interactions with the ion.
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