BSSE can be eliminated from the MBE(n) calculations by performing all subsystem calculations in the full-cluster basis set. 104 This is somewhat expensive and was pursued using a small basis set, with HF/6-31G and PBE/6-31G results shown in Fig. alongside conventional MBE(n) results that use only subsystem basis functions. The latter approach engenders significantly large errors and a -50 kcal/mol shift in the magnitude of the n-body corrections, for both HF and PBE. The CPcorrected HF/6-31G data (Fig. ) converge by n = 4. For PBE/6-31G, use of the full-cluster basis significantly dampens the magnitude of the oscillations yet they remain quite large, with errors of ∼ 20 kcal/mol at the n = 3 and n = 5 level, and errors that are comparable in magnitude but opposite in sign for n = 4 and n = 6. The difference between full-cluster HF and PBE results points to the interplay between SIE and BSSE. These effects are coupled because the loss of neighboring basis functions (when the full-cluster basis is replaced by a subsystem basis) confines electron density to a small number of monomers, preventing it from delocalizing throughout space. Similar artificial localization has been observed for anions, where SIE in semilocal functionals leads to an unbound electron that may become artificially bound in a finite basis set. Examples of the same effect include fractional charges on well-separated moieties and charge-sloshing leading to oscillations when MBE(n) is applied to proteins with charged side chains. As a result of SIE, the mere presence of a distant (therefore, non-interacting) system has a stabilizing effect on the total energy. In MBE(n), both proximate and distant systems are added and removed as n changes, resulting in dramatic overstabilization of higher-order nbody correction terms when the GGA functionals are used. This imbalance is somewhat mitigated by CP correction because the anion's charge can delocalize to other ghost atom sites in each of the subsystem calculations. Absent CP correction, aQZ basis functions extend only about 3 Å beyond the nuclei, 106 so cannot support a delocalized electron beyond the monomers that are present in the subsystem.