The magnitude of the associated free energy change is thus a strong function of the water adsorption energy, due to the large energetic cost to displace these additional water molecules. This "cost", however, must be balanced against the intrinsic gas-phase binding energy of the adsorbate. In the case of Cu and Ag, this cost is sufficiently high that the parallel binding mode becomes unfavorable, and the most stable mode becomes the perpendicular one. Beyond the change in the preferred binding mode, a significant reduction in the predicted binding free energy of 0.4~1.4 eV is also obtained for the adsorption of benzaldehyde at metal/water interfaces, depending on metal and adsorption geometry. A similar decrease in binding energy was previously noted by Liu et al. , who also attributed this decrease to competitive water adsorption. It is important to note that neither the large decrease in binding free energy nor the shift to the adsorption mode is predicted by ubiquitous continuum solvation models, which predict only very small changes (less than 0.1 eV) versus gas-phase calculations (see Fig. ). These results strongly support the contention that competitive water adsorption is essential in the free energy of adsorption at metal/water interfaces. Seeking to generalize these results, we further investigated the relationship between the competitive water adsorption and the solvation contribution to adsorption free energy with a selection of additional small organic molecules (benzene, naphthalene, pyridine, and furfural).