Pople's basis sets have been shown to be effective in describing strong orbital relaxation effects common in core-hole states 60 . The effect of triple excitations was accounted by additional CVS-EOM-IP-MLCC3 calculations for a smaller number of snapshots. There are two variants of CVS-EOM-CC approach, one in which the core is frozen at the CCSD step (fc-CVS-EOM-CCSD 41 ) and the one in which the core is active (CVS-EOM-CCSD ). Table II summarizes the results for the isolated water molecule (using ωB97X-D/aug-cc-pVTZ optimized structure). As one can see, the two versions of CVS-EOM-IP-CCSD differ by about 1 eV. At the CCSD level, fc-CVS-EOM-IP-CCSD is closer to the experiment due to fortuitous cancellation of errors, however, at the CC3 level, CVS-EOM-IP-CC3 yields a smaller error than fc-CVS-EOM-IP-CC3. The effect of triple excitations is -2.6 eV for both methods. Remarkably, even when triples are included, the computed IEs are red-shifted with respect to the experiment by 1-2 eV. The difference is too large to be attributed to the basis set effect-the benchmark 60 calculations for oxygen edge have yielded IEs with u6-311+G(3df) that were less than 0.1 eV from the estimated complete basis-set limit (at the CCSD level). Possible reasons could be the effect of the continuum 61 (neglected in the CVS scheme), zero-point vibrations, or relativistic effects. Despite these discrepancies in the absolute value of gas-phase IE, we anticipate much higher accuracy in ∆IE, as the errors should cancel out. In the simulations of the spectrum, we use fc-CVS-EOM-IP-CCSD and evaluate the effect of triple excitations to the shift by computing the difference between the ∆IE from CVS-EOM-IP-CCSD and CVS-EOM-IP-MLCC3.