τ 4 = 0.1 τ 3 maintains the absolute error within 1 kcal/mol at the expense of increased fragment counts. The latter settings retain most of the trimers, which are generated from the four-body overlaps, and this masks the influence of τ 3 . For top-down screening to be effective, both τ 3 and τ 4 must be tuned to strike a balance between accuracy and efficiency, where efficiency is measured by the fragment counts that appear in the lower panels of Fig. .