Molecular dynamics simulation of crystal dissolution from calcite steps

Molecular-dynamics simulations were used to model two stepped {10 (1) over bar 4} surfaces of the calcium carbonate polymorph calcite. The acute monatomic steps were found to be more stable than the obtuse monatomic steps. The initial stages of dissolution from the steps were considered in vacuo and in water. In vacuo CaCO3 was shown to dissolve preferentially from the obtuse step. In aqueous environment both stepped surfaces are stabilized by the presence of the water molecules although the relative stabilities remain similar. Using potential parameters that reproduce experimental enthalpies of the dissolution of calcite crystal, the formation of the double kinks on the obtuse step is shown to cost less energy than dissolution from the acute step, probably due to the lower stability of the obtuse surface. The simulations suggest that formation of thr kink sites on the dissolving edge of the obtuse step of calcite is the rate determining step and this edge is predicted to dissolve preferentially, which is in agreement with experimental findings of calcite dissolution under aqueous conditions. [S0163-1829(99)12039-3].