Development of a ReaxFF Reactive Force Field for NaSiO_x/Water Systems and Its Application to Sodium and Proton Self-Diffusion

Abstract

We present the development of a ReaxFF reactive force field for Na/Si/O/H interactions, which enables reactive molecular dynamics simulation of the sodium silicate–water interfaces. The force field parameters were fitted against various quantum mechanical calculations, including equations of state of different NaSiO x crystalline phases, energy barriers of a sodium cation’s transport within the sodium silicate crystal structure, interactions between the hydroxylated silica surface and sodium cation–water systems, and dissociation energies of [NaOH–n(H2O)] (n = 1–6) clusters. After the optimization process, we validated the force field capability through calculating the structures of sodium silicate crystals and glasses and transport properties of sodium ions and protons within the amorphous structures. The force field was also applied to validate the dissociation behavior of sodium hydroxides within the bulk water. Our results with the developed force field are relevant to detailed chemical dissolution mechanisms, which involve (a) the interdiffusion process of sodium ions from glasses and protons from water, (b) subsequent ionic self-diffusion of sodium ions from the subsurface region to vacancy sites at the glass–water interface, and (c) sodium ions interaction with water after leaching from the amorphous sodium silicate system.

Structural features of sodium silicate glasses from reactive force field‐based molecular dynamics simulations

“…As those defects can affect the reactivity of the local environment during the simulation of glass‐water interface, this can cause issue when performing simulations of glass‐water interfacial reactions. Therefore, the Hahn18‐OO set seems promising as it can both generate reasonable glass structure and produce reliable reactivity during the glass‐water interfacial reactions …”

“…We applied two versions of ReaxFF parameters for Na–Si–O systems, Yu version (named as Yu17) and recently developed Hahn version (named as Hahn18) of ReaxFF to simulate the sodium silicate composition (22.8 mol% Na 2 O‐77.2 mol% SiO 2 ). The results are then compared with the results from MD simulations using well‐tested Teter potential set …”

“…The glass structures generated by the Teter potential according to the above glass preparation process were used as the initial structures in the simulations of structure comparisons. The ReaxFF simulations were performed using two versions of ReaxFF parameters (Yu17 and Hahn18) and compared with reference Teter simulations. Three parallel tests have been performed for each simulation.…”

“…In order to simulate the interaction of sodium silicate glasses with water and the glass corrosion behaviors, a set of potential that can describe not only the glass structure but also the chemical reactions with water, as well as associated sodium ion diffusion and solvation in water, is needed. Recently, based on early development of silica‐water reactive force field (ReaxFF) potentials, a set of ReaxFF parameters for sodium silicate‐water system has been developed and refined to a wide range of first‐principles data including the equation of states of sodium silicate crystals, sodium ion migration in solids, sodium ion solvation, and Na‐OH dissociation in water . This potential provides an unprecedented opportunity to study the reactions of sodium silicate glasses with water.…”

Searching for correlations between vibrational spectral features and structural parameters of silicate glass network

“…Molecular dynamics simulations were carried out with three different types of potentials—Teter, MGFF, and ReaxFF Si/O/H/Na parameterization—and the most reasonable potential was chosen based on the comparison of theoretically calculated IR spectra with the experimental spectra. In the following, highlights of each potential are summarized and the reason for choosing these potentials is elucidated.…”