In Fig. , the absolute errors in the total energy compared to a supermolecular DFT calculation are plotted for both the eb-MFCC and eb-MFCC-MBE(2) schemes and for the corresponding density-based extensions of these schemes. In all cases, the conventional eb-MFCC scheme leads to rather large errors. For the two helices, the errors of 169 and 179 kJ/mol demonstrate the need of accounting for intramolecular interactions. For the turn, the error is smaller because there are fewer intramolecular hydrogen bonds, but with 72 kJ/mol, it is still substantial. Even for the β-strand, in which no intramolecular hydrogen bonds are present, the error still amounts to 17 kJ/mol. As reference, single-point calculations for the full polypeptides have been performed.