Here, the many-body expansion (MBE) provides a straightforward and systematically improvable fragmentation method. It approximates the total energy of a molecular cluster in terms of the energies of monomers, dimers, trimers and so on. These can each be calculated with accurate quantum-chemical methods such as CCSD(T). If this expansion can be truncated at sufficiently low order -preferably already at the two-body level (i.e., requiring only calculations for monomers and dimers) -it provides an attractive scheme for overcoming the steep scaling of the computational effort with coupled-cluster methods (for impressive examples, see Ref. 26,27). Moreover, the individual fragment calculations can be executed in a massively parallel fashion (see, e.g., Ref. 28).