A Computational Study of Silica Dimerization Reaction

We studied silica dimerization reactions in the gas and aqueous phase by density functional theory (DFT) calculations and reactive force fields (ReaxFF). This process involves the formation of five- coordinated silicate complex as an essential intermediate in the condensation reaction. We examined the reactions in the gas phase using constrained energy minimizations along different steps along the reaction coordinate and compared DFT calculations with two ReaxFF parameter sets. We find that energy differences are rather large even at unreactive conditions in which the silicate molecules are relatively far away. To test the effect of the discrepancies in energies we also launched molecular dynamics simulations using DFT and ReaxFF and, indeed, we observe unphysical reactions for both ReaxFF forcefields. Our results suggest that the standard procedures for parameter fitting need to be changed in order to make reactive forcefields more reliable.