Here we investigate the accuracy of both the pure CP 3 and the mixed M2P2/CP 3 model with varying cutoff distances using properties computed using a full MFCC-based M2P2 potential as the reference. The results are presented in Figures . The cutoff in case of mixed M2P2/CP 3 defines the distance from the quantum region up to which the M2P2 potential is used while the CP 3 is used for the remaining amino-acid residues. Thus, a distance of 0.0 Å corresponds to pure CP 3 . We also compare to a conventional cutoff approach where the MFCC-based M2P2 potential is used up to a cutoff distance while the remainder is neglected, which is an alternative approach to reduce computational cost. In general, we find that a mixed M2P2/CP 3 representation of the protein with an appropriately chosen cutoff can provide properties with essentially the same accuracy as a full M2P2 treatment. However, using a pure CP 3 description of the protein or a mixed M2P2/CP 3 description with a too short cutoff distance can lead to relatively large errors in some cases.