The EA-TDDFT spectra in Fig. show the same qualitative features as those calculated using CCSD, including the significant drop in intensity in the range 406-411 eV for NH 3 •(H 2 O) 4 and 409-414 eV for NH + 4 •(H 2 O) 4 . While the CCSD calculations were truncated at 30 roots, the EA-TDDFT calculations were not truncated, suggesting that this decline in intensity is a true feature of the four-explicit-water spectrum. Overall, the features of the post-edge are not adequately captured by EA-TDDFT or CCSD if only four explicit water molecules are used, but the spectra in Fig. that contain two hydration shells clearly approximate the bulk spectrum very closely. The EA-TDDFT results also overemphasize some of the pre-edge features in both spectra relative to CCSD, which in itself is undesirable. Failure of both EA-TDDFT and CCSD in the post-edge region implies that the four-water model is too small to reliably predict solution-phase XAS, and that the most likely culprit for the small post-edge tail in the TP-DFT results is an inadequate representation of the hydration environment (though, other features depend strongly on the TP-DFT model in question). Instead, this points towards the interesting conclusion that the long post-edge tails in NH 3 and NH + 4 are a result of many-water cooperativity. It is sensible that the post-edge tails depend on many explicit water molecules because the orbitals that contribute to excitations in this high-energy regime are extremely delocalized. Without a sizable number of explicit water molecules, the model cannot accurately describe the extended nature of the excited states that comprise the post-edge tail. The role of the choice of basis set (atom-centered versus plane-wave) on the post-edge features is an interesting avenue for future work.