Quantum, classical, and multi-scale simulation of silica–water interaction: molecules, clusters, and extended systems

Abstract

Over the past 6 years, we have engaged in a multi-faceted computational investigation of water-silica interactions at the fundamental physical and chemical level. This effort has necessitated development and implementation of simulation methods including high-accuracy quantum mechanical approaches, classical molecular dynamics, finite element techniques, and multi-scale modeling. We have found that water and silica can interact via either hydration or hydroxylation. Depending on physical conditions, the former process can be weak (<0.2 eV) or strong (near 1.0 eV). Compared to hydration, the latter process yields much larger energy gains (2-3 eV/water). Some hydroxylated silica systems can accept more water molecules and undergo further hydroxylation. We have also studied the role of external stress, effects of finite silica system size, different numbers of water molecules, and temperature dependences.

Molecular dynamics simulation of nanocolloidal amorphous silica particles: Part I

“…This study has successfully modelled the interactions between, and near-surface structure of, amorphous silica nanoparticles in aqueous solutions with varying amounts of background counter-ions using realistic molecular dynamics force fields, evaluating the interparticle potentials using a PMF formalism. This work shows that water molecules can penetrate into amorphous silica nanocolloid particles, and that 'hairiness' of the silica surface (modelled at atomic resolution with a realistic silica surface structure) has an effect on the interparticle potential of mean force, in agreement with other work in the literature [17,18], describing a thin 'hairy' layer on the surfaces of such systems. The consequences for water ordering has also been investigated, in conjunction with the presence of surface-bound and free background counter-ions.…”

“…Theoretical models for property prediction have been developed covering a wide range of length and time scales, Ab-initio studies of nucleation [6,7] and stability of oligomers [8][9][10][11] have been carried out; molecular dynamics using reactive potentials has also been used in similar studies [12][13][14][15]. In recent years, some multiscale studies on silica systems have also been carried out [16][17][18]. A number of mesoscale approaches to colloidal structure and dynamics such as Monte-Carlo, Brownian dynamics etc.…”

Evaluating Water Reactivity at Silica Surfaces Using Reactive Potentials

“…Water and silica are among the most abundant compounds in the earth’s crust and surface, and the study of interactions between the two have significant implications in geosciences, glass technology, nuclear sciences, biomaterials, and biological systems. As a consequence, there is a scientific interest in understanding the interactions between the two in a wide range of length and time scales and research in this field has been in progress for several decades now. , Computational modeling of these interactions has been done in a variety of methods including ab initio, density functional theory (DFT), and semiempirical quantum mechanical (QM) methods in the atomistic and angstrom scales, − classical molecular dynamics (MD) simulations up to multiple − nanometers scale, and greater lengths through multiscale methods. − …”

“…There is an even greater number of models for classical potentials for simulations of water (ref and references therein); however, most of these water potentials were designed for simulation of a narrow range of physical properties of water. An important aspect of silica–water interactions is the hydrolysis reaction that leads to the formation of silanols and dissociation of water molecules which would control several other chemical interactions in the system. ,, This chemical reaction can be reproduced either by ab initio QM calculations ,, or by combining classical MD potentials and QM calculations, ,,, but such simulations are limited in size due to the computational complexity involved. Classical MD simulations using reactive potentials enable study of the effect of medium-range structure features and relaxation due to surface and bulk effect.…”

Working at the interface

“…Step 3: the second molecule shares a proton with an O atom in silica after being in a transient state Our studies [38][39][40][41][42][43][44] showed that this two-water process is a general feature of the water-silica interaction. Purely due to the size of H 2 O and the Si-O bond length, the reaction barrier is lowered significantly by the collective motion of the two water molecules.…”