Supplement NUmber 1

Raw simulated data for densities, viscosities, surface tension and temperature of maximum in density; Representative site-site radial distribution functions. TMD data for the HCl model with $q=\pm0.75e$. \textit{Topology} file for GROMACS with optimized potential parameters of H$_3$O$^+$. \textit{Topology} file for GROMACS with optimized potential parameters of HCl with $q=\pm0.75e$.