Table : Errors in the protein-ligand interaction energy (ADF/BLYP/DZP) for the conventional MFCC method and the MFCC-MBE(2) method for a test set of seven proteinligand complexes. We include results both with a COSMO solvation model using ε = 4 and ε = 78.39 (water). All values in kJ/mol. The MFCC-MBE The reference protein-ligand interaction energies calculated in full, supermolecular calculations are listed in Table . The largest interaction energies are obtained for the multiply charged sulfate and phosphate ions as ligands (i.e., for 1AAL and 1A6F), where they amount to 3392 and 5046 kJ/mol, respectively. For cases in which the ligands are deprotonated acids with a single negative charge (i.e., for 1ABA, 1STP, 1TOW, and 2IFB), interaction energies between 200 and 600 kJ/mol are obtained, whereas with the zwitterionic ligand in 2PK4, the calculated interaction energy amounts to 683 kJ/mol (for ε = 4)