The adsorption behavior of a single and multi-water molecules on tricalcium silicate (111) surface from DFT calculations

The interaction between water and tricalcium silicate (C3S) is important for the portland cement hydration, but the description at the atomistic level is still unclear. In this work, we investigate a single and multi-water molecules adsorption behavior on tricalcium silicate (111) surface using DFT approach. For a single water molecule, both molecular and dissociative adsorption of a single water molecule can occur on the calcium silicate (111) surface and the dissociative state is preferred. The dissociative adsorption of water can only occur on the ionic O atoms while molecular adsorption can be found on the Ca atoms. The higher reactivity of ionic O atoms can be explained by the significant contribution of the O-i-2p orbital in the valence band maximum of the surface slab. The surface reconstruction leading by dissociative adsorption is more significant than that of molecular adsorption. For two or three water molecules adsorbing on one surface unit cell, full dissociative adsorption is the most energetic mode. For 4-15 water molecules, a mixed adsorption mode is found to be favorable. As the water coverage increase, the stepwise adsorption of water decreases due to the interaction between adsorbed water molecules.