∆A 2 can be easily calculated as 2.029 eV at the standard state using the FP method with the revised Perdew-Burke-Ernzerhof semi-local functional, 61 augmented with Grimme's dispersion interaction (RPBE+D3), and the ideal gas model. However, ∆A 1 cannot be represented by simple statistical models and requires computationally intensive numerical calculations of statistical averages over phase space for interfacial water, which takes nanoseconds to reorient. To accurately obtain ∆A 1 , we use the MLFF-assisted TI calculations from a non-interacting hydrogen atom to an interacting one at the interface: