While we only performed DFT calculations in the present study, the db-MBE can be combined with other quantum-chemical methods, in particular with accurate wavefunctionbased methods. As the number of monomer and dimer calculations required for the db-MBE(2) scales only quadratically with the number of fragments while retaining excellent accuracy, it might allow us to overcome the scaling bottleneck of accurate wavefunctionbased quantum chemistry. This will enable the efficient, yet accurate treatment of large ion-water clusters and possibly also of condensed-phase systems with the db-MBE .