Car-Parrinello molecular dynamics simulations of Na^{+}-Cl^{-} ion pair in liquid water

Abstract

The aqueous solvation shell of a Na + –Cl − pair is studied using Car-Parri-nello molecular dynamics simulations. Water-mediated and contact states of the ion pair are investigated. The first hydration shell of the Na + 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 − ion. The first hydration shell of the Cl − is less structured and strongly effected by the proximity of the Na + in the contact state. The oxygen coordination numbers for Na + and Cl − 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.