Titration is performed by adding NaOH base to the system. Since hydrolysis of water is so weak, addition of one OH -will result in a reaction with hydronium ion inside the cell and appearance of a new water molecule. Within the present implicit water model, addition of one sodium hydroxide molecule is then equivalent to replacing one proton inside the simulation cell with a sodium ion, H + -→Na + . Therefore, to vary pH, we simply replace one of the protons by Na + and rerun the simulation. This will result in a new polyelectrolyte charge and new equilibrium pH. Repeating this procedure until all protons inside the cell have been replaced by sodium ions, we obtain the full titration curve.