where E supersys is a conventional supramolecular calculation at the "target" level of theory that is used for the MBE(n) terms. From Fig. (a) we find that MBE(3) maintains subkcal/mol accuracy provided that τ 3 ≤ 0.1 kcal/mol, whereas for larger values there is a rapid increase in the error as the screening becomes too aggressive. This loss of accuracy for τ 3 > 0.1 kcal/mol is substantially mitigated by moving to a four-body expansion. This is true for all values of τ 4 that we test, although the most restrictive value (τ 4 = 0.2 τ 3 ) does exhibit absolute errors exceeding 1 kcal/mol when τ 3 > 0.1 kcal/mol Setting ) with M = 0, 1, or 2. (The screening algorithm is fully specified by τ 3 and M so there is no τ 4 in the bottom-up approach.) Lower panels (e)-(h) show the mean fragment counts in the form of stacked plots.