To understand what is required in order to obtain converged values of ∆E int , we first study the behavior of MBE(2) as a function of R cut . Results for the 2,636-atom 181L system that was considered in Section 3 .1 .1 are shown in Fig. , examining how MBE(2) converges with respect to R cut , the distance threshold for discarding subsystems. Previously, we showed that R cut = 8 Å affords converged thermochemistry for a 632-atom model of a different enzyme, exploring several functional and basis-set combinations. (This 632-atom model affords converged results with respect to larger radial models of the same enzyme. 116 ) The value R cut = 8 Å also works well here. Increasing it to Fig. : Interaction energies ∆Eint for the benzene ligand in 181L, computed using MBE(2) at the indicated levels of theory, using a distance cutoff (Rcut) to cull the dimers that are included in the calculation.