Absolute redox potential of liquid water: a first-principles theory

A first-principles molecular dynamics method is proposed to calculate the absolute redox potentials of liquid water. The key of the method is the evaluation of the difference between the vacuum level and the average electrostatic potential inside liquid water, which employs an average over both space and time. By avoiding the explicit use of the Kohn-Sham levels, such as the position of the valence band maximum, as the reference energy for the excited electrons, we are able to calculate water redox potentials accurately using a semi-local density functional and an entropic contribution estimated from experimental data.