A density functional theory based study of the microscopic structure and dynamics of aqueous HCl solutions.

The aqueous solvation of hydrochloric acid is studied using density functional theory based molecular dynamics simulations at two concentrations. The large simulation boxes that we use allow us to investigate larger-scale structures such as the water-bridged chloride ion network. We find a strong concentration dependence for almost all structural and dynamical properties. Excess protons are mostly present both as Eigen and Zundel structures, either as a direct hydronium-chloride contact-ion pair or a solvent-separated ion pair. Increasing the concentration has a detrimental effect on the natural hydrogen bonded network of water molecules. This effect is visible in our studies as a decrease in the persistence time of the solvation shells around the chloride ions. Also the number of proton hops, determined by a new and well defined identification procedure, suffers from the breakdown of the natural hydrogen bond network.