The first two terms in eq. 6 represent the free energy contributions from the individual PMF calculations (separation, conformational, orientational and positional restraints in the bound state, and conformational restraints in the unbound state). The last term in eq. 6 is a correction that accounts for the release of the ligand to the standard state surface area after dissociation from the receptor; it corrects for the release of all angular restraints in the bulk solvent: