The water-calcite interface is investigated with theoretical calculations based on classic molecular dynamics (MD) and Car-Parrinello molecular dynamics (CPMD), and XPS experiments have been also employed to study water dissociation at the interface. The MD simulation results show that the hydrogen bonds between water and carbonate groups, and the electrostatic interactions between water and calcium ions are the major interactions at the interface. Furthermore, Metadynamics has been used with CPMD calculations to explore the free energy surface of water on the calcite surface, and an energy barrier of 300 kJ/mol is predicted for the water dissociation on the calcite surface, which suggests such dissociation process will rarely take place under normal conditions. However it also shows the calcite surface can stabilized derivatives from the dissociation reaction at the interface. A constrained CPMD calculation is implemented to drive water to dissociate on the calcite surface, and the result suggests that external energy input could overcome the energy barrier for water to dissociate, and form HCO3 at the calcite surface. The XPS experiments at ultra high vacuum (UHV) conform that water will be dissociated and approximately 45% CO3 groups at the first layer will be transformed to HCO3 after 3 hours.
