This product is over all pairs of monomers s and s , and leads to all possible combinations of monomer pairs in the sum. The only exception is the part of the sum that only is the product of the 'ones', and cancels out with the -1 in the overall f -bond expression. Of particular interest to the RPA calculation are the terms that consist of only (1) a single factor f α,γ (r i,α (s), r j,γ (s )) that goes between any pair s and s on chains α and γ, and (