Computer simulations do not support Cl-Cl pairing in aqueous NaCl solution

Ion-ion correlation functions of a 5M NaCl-SPC water model were calculated by molecular dynamics and Monte Carlo simulations. No paired anions were found in contradiction with the extended reference-interaction-site model theory predicting Cl-Cl pairs for the same model. In order to check for a possible water model dependence the transferable interacting point sites model was also considered. Calculations for a 5 M solution using molecular dynamics and for a single chloride pair in water using constrained molecular dynamics again did not show the formation of anion pairs in contact