Calculations on (H 2 O) 20 and (H 2 O) 32 clusters were performed at the ωB97X-V/def2-TZVPD level with a supersystem correction at the level of Hartree-Fock (HF)/ def2-TZVPD. Calculations on (H 2 O) 64 were performed at the level of second-order Møller-Plesset perturbation theory (MP2), using the jun-cc-pVDZ basis set and a resolution of identity (RI) approximation, in conjunction with a supersystem correction at the HF/jun-cc-pVDZ level.