Cleavage and recovery of molecular water in silica.

ABSTRACT

The network response associated with the incorporation and reactivity of water molecules in bulk phases of amorphous and crystalline silica are investigated using density functional theory. The extent of network relaxation is found to change the relative stabilities of the reactant and product states. A highly reactive site, with a low activation barrier, is associated with a highly strained site in which network relaxation significantly stabilizes the silanol state by effectively annealing the local structure. Diffusion and exchange reaction paths are found to likely be associated with minimum energy paths in which the stability of the product and reactant states are equal. These latter paths are associated with minimal network response, although the ability of the silanol groups to take on several conformations has an overall effect of changing the stability along a given reaction path.