Density-functional study of chemical reactions at a solid-fluid interface: passivation of the (0001) surface of Cr$_2$O$_3$

Using a new form of density functional theory for the {\em ab initio} description of electronic systems in contact with a dielectric environment, we present the first detailed study of the impact of a solvent on the surface chemistry of Cr$_2$O$_3$, the passivating layer of stainless steel alloys. Compared to vacuum, we predict that the presence of water has little impact on the adsorption of chloride ions to the oxygen-terminated surface but a dramatic effect on the binding of hydrogen to that surface. These results indicate that the dielectric screening properties of water are important to the passivating effects of the oxygen-terminated surface.