The purpose of this proposal is to use accurate first-principles quantummechanical methods to study the reactions of aqueous fluids with simple mineral surfaces at the atomic level. I aim to describe and quantify the surface reaction mechanisms taking part in the dissolution of CaCO and CaO. The calculations will examine both physisorption and dissociative 3 chemisorption of H20 molecules, H O and OH ions both on the perfect cleavage surfaces and defective surfaces. Plane-wave pseudopotential calculations conducted on workstations and supercomputers will allow a realistic model of the fluid/surface environment. The computations will yield accurate predictions of adsorption and dissociation enthalpies, and activation energies for the detachment reaction, and help to explain the factors influencing the kinetics of dissolution.