Consider now a closed system containing polyions with titratable surface groups, salt, and acid. We can start the system in a initial state in which all polyelectrolyte groups are com-pletely deprotonated, with the corresponding number of hydronium ions placed in the bulk of the simulation cell. The cell also contain ions derived from the dissociation of salt, say Na + and Cl -. The reactive MC simulation then determines how many of polyelectrolyte groups will become protonated in equilibrium. The acceptance probabilities for deprotonation/protonation moves are given by 44,48-50