As a final comment, we notice from the comparison of XA spectra obtained using different QM regions in the XFH QM/MM calculations in Figure , that limiting the QM region gives rise to finite size effects in the XA spectra with feature appearing 2-3 eV above the main edge for both solutes. These features are smeared in the case of a larger QM region due to orbital mixing with the surrounding water molecules. However, the post-edge features in the PE-CCSD QM/MM calculations are further up in energy and, in the case of ammonium, they align nicely with the position of the experimental post-edge feature. Hence, we deem this to be a significant improvement in the CCSD treatment and not an artifact of the QM/MM approximation.