Fracture, water dissociation, and proton conduction in SiO2 nanochains

A basic issue in nanoscale systems is whether large-scale behavior occurs or not. At and above the mesoscale, the water-silica interaction is known to have large effects, e.g., the geological importance of hydrolytic weakening. Here, we show that water not only substantially weakens a silica nanochain that has been the focus of much recent research but also leads to novel proton conduction. The SiO2 chain consists of a string of orthogonal (planes alternating vertically and horizontally) two-membered rings. We treat two cases of adjacent water to understand both local and collective motion in the system. The first is two water molecules, the second is a water monolayer film that coats the entire chain. Structure, charge separation, stress dependent bond breaking and formation, and proton conduction are discussed based on results obtained at the room temperature. The simulations have been performed using both first-principles molecular dynamics and a novel multiscale quantum-classical software system.