The last definition of Eq. ( ) indicates that ∆∆G φ,solv accounts for the difference between the desolvation free energy of the unary-to-binary binding and the sum of the desolvation free energies from two pairwise binding events. In other words, the cooperative solvation contribution might be non-zero if the two ligand-protein binding interfaces are spatially close to each other (Figure ), and becomes gradually negligible when the two interfaces get further apart with the two desolvation events being independent (Figure ) of each other. In the rigid body and fixed-charge description, semi-analytical methods can further show that ∆∆G φ,solv stems predominantly from atoms at the three-body interface (see Section S3 in the Supporting Information). In the stabilized conformational space, the cooperative solvation contribution is described by ∆∆G s φ,solv .