| Summary: | The aqueous solvation shell of a Na<sup>+</sup>-Cl<sup>-</sup> pair is studied using Car-Parrinello molecular dynamics simulations. Water-mediated and contact states of the ion pair are investigated. The first hydration shell of the Na<sup>+</sup> ion is found to be octahedral with one vacant position for both states. In the contact state one of the water molecules is substituted by the Cl<sup>-</sup> ion. The first hydration shell of the Cl<sup>-</sup> is less structured and strongly effected by the proximity of the Na<sup>+</sup> in the contact state. The oxygen coordination numbers for Na<sup>+</sup> and Cl<sup>-</sup> are 4.9 and 5.6 for the water-mediated state, and 3.6 and 6.4 for the contact state. The corresponding hydrogen coordination numbers are 10.9 and 5.2; 9.2 and 3.9, respectively.
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