Before discussing the combination of MFCC with the MBE, we first consider a simplified variant of the MFCC method, in which hydrogen atoms are used as caps . In this case, the cap molecule is a dihydrogen molecule (see Fig. ). We denote this variant by the acronym H-MFCC in the following. Note that in this variant, the electronic structure of the peptide bond is severely altered in the capped fragments compared to the original protein. Therefore, H-MFCC cannot be expected to perform well, but it is considered here because it simplifies the inclusion of two-body terms. Note that other fragmentation schemes for proteins that use hydrogen caps do not cut the peptide bond, but cut the carbonyl-C α bonds instead. Assuming that the additional interactions introduced by the hydrogen caps are small, it becomes straight-forward to formulate a two-body correction that can be applied on top of the H-MFCC by only considering fragment-fragment (ff) interactions, i.e.,