Accurate and Efficient Prediction of pKa in Aqueous Electrolytes Using Local Electrostatic Potentials

The Kw=10^-pKw in aqueous electrolytes exhibit significant variations as a function of ion concentration. This behavior is not well-described by the Pitzer model, particularly at high concentrations. Here, we provide a molecular interpretation of the concentration dependent trends in pKw and develop a new method that accurately predicts the dissociation constant based upon the local electrostatic potential of the water oxygen that is determined by its nearest neighbors. The method is computationally efficient, relying only upon sampling of the local configurations (via molecular dynamics) and a small set of experimentally measured pKw. It is extensible to a range of salt compositions and the molecular understanding of the local potentials provides new routes toward the development of electrolytes with tailored physicochemical properties like pKw.