The remaining analysis focuses on two-body interactions because MBE(2) can be used for rapid screening and to evaluate convergence of binding-site models. Figure provides a closer look at the two-body terms computed at the HF-3c level, organized into histograms for each of four protein-ligand complexes . These histograms include only those terms |∆E I,ligand |, meaning that one of the fragments is the ligand. Each distribution in Fig. is asymmetric about zero. Additionally, there does not seem to be a single energy threshold that would be viable across all four of these systems, as the energy scale for |∆E I,ligand | is rather different in each of the four examples.