As for the previous test cases, it is obvious from Fig. that the use of a suitable embedding potential is essential for ion-water clusters. For the isolated eb-MBEs and db- Included are results from both the isolated MBEs ("iso") and the embedded MBEs using point-charge embedding ("PC") as well as using frozendensity embedding with the unrelaxed frozen densities of the isolated fragments ("FDE") and a relaxed frozen density obtained using freeze-and-thaw cycles ("FDE-ft"). Some data points might lie outside the shown energy range. However, the embedded eb-MBE( ) is not able to reproduce the correct ordering of the isomers at all. For the most accurate FDE-ft embedding, the mean and maximum errors in the relative interaction energies still amount to 8 kJ/mol and 17 kJ/mol, respectively.