In some of the calculations presented below, distancebased screening is used to reduce the number of subsystem calculations required for MBE(n). In that case, subsystems are omitted if the minimum interatomic distance between any two fragments exceeds a specified threshold, R cut . In previous work on protein fragmentation, we showed that R cut = 8 Å affords results that are converged (with sub-kcal/mol fidelity) with respect to the equivalent MBE(n) calculation performed using all possible subsystems. As an example of the cost savings that is engendered, consider the T4-lysozyme with the protein data bank (PDB) code 181L, which is one of the systems considered below. In that case, N frag = 164 for the entire protein system but the use of R cut = 8 Å reduces the number of subsystems for a MBE(3) calculation from 708,561 to 16,016, a 98% reduction.