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

The K_w = 10^-pK_w 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 pK_w and develop a new method that accurately predicts the dissociation constant based on the local electrostatic potential of the water oxygen that is determined by water nearest neighbors. The method is computationally efficient, relying upon sampling of only the local configurations (via molecular dynamics) and a small set of experimentally measured pK_w. 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 pK_w.