To confirm the accurate creation of a hydrated electron in our simulations, we calculated its radius of gyration (r g ), which is a rigorous metric that can be experimentally measured or calculated with AIMD simulations. In short, the radius of gyration is a tensor describing the second moment of positions of a collection of particles. In our study, the radius of gyration was calculated from the spin density of the hydrated electron, and further details of our calculations are given in the Supporting Information. Our calculated average r g values for a hydrated electron in explicitly solvated PFOA and PFOS are 2.46 and 2.45 Å, respectively, which are in close agreement with previous experimental (2.50 Å) and theoretical (2.16 -2.65 Å) studies.