We can understand the minor influence of the excess electron on the cavity XAS transitions by determining the effect of an added electron on the p and h energies, following the definition of Ref. 43. Here, we consider transitions from firstshell waters only, since they dominate the spectrum. As we see from Fig. , the excess electron destabilizes the p and h states by similar amounts, largely explaining the insensitivity of the XAS transitions to the presence of the excess electron. We note an additional destabilization of the p by approximately +0.8 eV relative to the h, which is consistent with the p occupying the same cavity as the excess electron, while the h state is localized to a single first-solvation shell O1s core. However, the XAS transitions are not simply the difference between the p and h energies, since this neglects p-h interactions. Indeed, we find that on average, the p state is closer to the h than the electron is (2.0 and 2.7 Å respectively), 44 leading to p-h Coulomb binding energies of 5.6 and 5.3 eV in the XAS transitions of e - (aq) and the neutral calculations respectively. The remaining 0.5 eV difference between the anionic and neutral system can be assigned to exchange and correlation contributions to the p-h interaction (see section S-V.4). The substantial p-h attraction thus compensates the repulsion experienced from the excess electron, leading to a particle state with a binding energy similar to that of e - (aq) (see Fig. ) and this explains the overall small influence of the excess electron on the cavity XAS transition energies.