g 20 water molecules are treated by CCSD, the rest by MM charges Table shows the effect of triple excitation and different types of embedding evaluated for the same snapshot as used in Fig. . The u6-311+G(3df) basis was used on 5 waters and 6-31G on the rest of quantum waters. Although the absolute values of IEs vary between the methods, the value of the shift, ∆IE, is rather insensitive to the type of embedding, CVS scheme, or correlation treatment. The effect of MM charges (beyond 20 quantum waters) is about 0.1 eV and the effect of freezing the second solvation shell (15 water molecules) at the Hartree-Fock level of theory is approximately 0.1 eV (decreasing the magnitude of the red shift). The effect of including triple excitations with MLCC3 is almost 0.4 eV (increasing the magnitude of the red shift) for this snapshot. The multilevel framework makes it possible to use approximate triples for a study such as this, however, the cost remains a limitation and performing such calculation for hundreds of snapshots is impractical. We therefore use a subset of 40 snapshots to estimate the effect of approximate triples; the results are shown in Figure . The average shift is -0.34 eV, with a 0.07 eV standard deviation. This correction will be applied to the final averaged fc-CVS-EOM-CCSD result to provide our best estimate for the ∆IE.