To evaluate the efficacy of bottom-up energy screening using larger systems, a similar analysis is presented for (H 2 O) 32 clusters in Fig. and for (H 2 O) 64 clusters in Fig. . In order to make a direct comparison to results presented above, we use the same levels of theory for (H 2 O) 32 as for the (H 2 O) 20 clusters. However, calculations for (H 2 O) 64 are performed at a level of theory that constitutes a more realistic use case for MBE(n), with subsystem calculations evaluated at the RIMP2/jun-cc-pVDZ level of theory in conjunction with a HF/jun-cc-pVDZ supersystem correction. Error is then measured relative to a supersystem calculation at the RIMP2/juncc-pVDZ level. As demonstrated in previous energyscreened MBE(3) calculations, this results in dramatic speedups without large-scale parallelization, despite the need for of a supersystem HF calculation, while maintaining 1 kcal/mol fidelity for relative energies. Moreover, these (H 2 O) 64 calculations represents the largest application of MBE(4) in electronic structure theory of which we are aware.