Modeling adsorption at the metal/water interfaces is a cornerstone towards an improved understanding in a variety of fields from heterogeneous catalysis to corrosion. We propose and validate a hybrid scheme that combines the adsorption free energies obtained in gas phase at the DFT level with the variation in solvation from the bulk phase to the interface evaluated using a molecular mechanics based alchemical transformation, denoted MMsolv. Using the GAL17 force field for the platinum/water interaction, we retrieve a qualitatively correct interaction energy of the water solvent at the interface. This interaction is of near chemisorption character and thus challenging, both for the alchemical transformation, but also for the fixed point-charge electrostatics. Our scheme passes through a state characterized by a well-behaved physisorption potential for the Pt(111)/H 2 O interaction to converge the free energy difference. The workflow is implemented in the freely available SolvHybrid package. We first assess the adsorption of a water molecule at the Pt/water interface, which turns out to be a stringent test. The intrinsic error of our QM-MM hybrid scheme is limited to 6 kcal/mol through the introduction of a correction term to attenuate the electrostatic interaction between near-chemisorbed water molecules and the underlying Pt atoms. Next, we show that the MMsolv solvation free energy of Pt (-0.46 J/m 2) is in good agreement with the experimental estimate (-0.32 J/m 2). Furthermore, we show that the entropy contribution at room temperature is roughly of equal magnitude as the free energy, but with opposite sign. Finally, we compute the adsorption energy of benzene and phenol at the Pt(111)/water interface, one of the rare systems for which experimental data are available. In qualitative agreement with experiment, but in stark contrast with a standard implicit solvent model, the adsorption of these aromatic molecules is strongly reduced (i.e., less exothermic by ~30 and 40 kcal/mol for our QM/MM hybrid scheme and experiment, respectively, but ~0 with the implicit solvent) at the solid/liquid compared to the solid/gas interface. This reduction is mainly due to the competition between the organic adsorbate and the solvent for adsorption on the metallic surface. The semi-quantitative agreement with experimental estimates for the adsorption energy of aromatic molecules thus validates the soundness of our hybrid QM-MM scheme. File list (2) download file view on ChemRxiv SolvHybrid.pdf (20.52 MiB) download file view on ChemRxiv SI-SolvHybrid.pdf (705.65 KiB)

The kinetic stability of any material in water relies on the presence of surface weak spots responsible for chemical weathering by hydrolysis. Being able to identify the atomistic nature of these sites and the first steps of transformation is therefore critical to master the decomposition processes. This is the challenge that we tackle here: combining experimental and modeling studies we investigate the stability of alumina in water. Exploring the reactivity of shape-controlled crystals, we identify experimentally a specific facet as the location of the weak spots. Using biased ab initio molecular dynamics, we recognize this weak spot as a surface exposed tetra-coordinated Al atom and further provide a detailed mechanism of the first steps of hydrolysis. This understanding is of great importance to heterogeneous catalysis where alumina is a major support. Furthermore, it paves the way to atomistic understanding of interfacial reactions, at the crossroad of a variety of fields of research.