Fragmentation methods , which partition such clusters into their molecular constituents, offer an attractive approach for overcoming this bottleneck. The most straightforward realization of such a fragmentation method is the well-known many-body expansion (MBE) (see, e.g., Refs. , which approaches the total interaction energy of a molecular cluster as a sum of n-mer (dimer, trimer, tetramer etc.) interaction energy contributions. If the MBE can be truncated at a sufficiently low order, it provides a low-scaling and highly parallelizable computational approach for the accurate quantumchemical treatment of molecular clusters. Generally, a truncation at second order (i.e., a two-body expansion) would be highly desirable. In addition, the MBE provides the basis for the development of accurate force-field models, in particular for water and ion-water systems .