To assess the efficiency of our implementation of the SS-FNO-IP-EOM-CCSD* method, we have performed calculations on a series of water clusters ((H2O)n, n = 1-7) using the aug-cc-pVTZ basis set. We have specifically focused on determining the highest core ionization energy for each cluster size. The correlation calculations are carried out using the SS-FNO and canonical IP-EOM-CCSD methods. The computational time required for these calculations is measured and plotted against the cluster size in Figure . The calculations are conducted on a dedicated node equipped with 16 cores, featuring eight Intel(R) Xeon(R) Silver 4210R CPU @ 2.40GHz and 377 GB of total RAM. The results obtained from the plot indicate that the computational cost of the SS-FNO-IP-EOM-CCSD* method increases at a much slower rate compared to the canonical version as the cluster size grows. This suggests that the SS-FNO-IP-EOM-CCSD* method offers a more efficient approach for studying large molecules.