We also wish to avoid complicated capping schemes, as in "molecular fragmentation with conjugate caps" (MFCC). The "conjugate caps" amount to the backbone of the neighboring amino acid residue, the size of which makes MFCC difficult to generalize to arbitrary n-body interactions. In contrast, we have found that MBE(n) with simple hydrogen-atom caps can be used to obtain converged thermochemical quantities for enzymatic reactions. Lastly, we desire a method that can be applied to enzymes in their native protonation states, so that the ability to describe ions (and to use diffuse basis functions) is required. In fragment-based calculations, ionizable side chains are often protonated so as to obtain charge-neutral fragments, as this minimizes manybody polarization effects. However, there is no guarantee that the neutralized enzyme remains functional.