Silica–water model using the Vashishta force field

Abstract

Nanoscale interactions between silica (SiO2) and water (H2O) significantly influence the behavior of materials such as rocks, glasses, ceramics, and cements in geological and engineered environments. Accurate simulation of these interfacial phenomena requires force fields capable of describing bond breaking and formation. Here, we present a new parameterization of a classical dissociative force field specifically for molecular dynamics simulations of the silica-water system, based on the Vashishta potential functional form for bulk water, bulk silica, and their interface. A bond-order scheme distinguishes between oxygen in silica and oxygen in water. Silica-water interaction parameters were determined using a hierarchical genetic algorithm to reproduce the orthosilicic acid structure and silanol concentration on a silica surface. The model is validated against the energetics of the interface, yielding a calculated heat of immersion of 0.48(8) J m-2, within the range of experimental values for amorphous silica. The potential captures fundamental surface reaction pathways, such as water dissociation and the formation of isolated, geminal, and vicinal silanol groups, despite these mechanisms not being included in the training set. Applied to dynamic fracture simulation of wet silica, the force field reveals three main effects of water: reduced tensile strength, reduced toughness, and an altered failure mechanism-consistent with the molecular picture of hydrolytic weakening. This dissociative force field enables broader studies of chemo-mechanical processes, such as dissolution, friction, and hydrolytic weakening of silica in aqueous environments, under a wide range of thermodynamic conditions, while its computational efficiency allows for large-scale, long-timescale simulations.