Atomistic simulation of oxide surfaces and their reactivity with water

Abstract

Atomistic simulation is a valuable tool for interpreting and predicting surface structures. This paper describes our current work aimed at applying this approach to model oxide surfaces in contact with water. The atomistic simulation techniques used are energy minimisation and molecular dynamics, which are coupled with interatomic potentials. Energy minimisation allows us to evaluate the most stable surface configurations and molecular dynamics provides the effect of temperature on the surface. The use of interatomic potentials, which describe the forces between the atoms, allows the surface properties to be calculated rapidly hence enabling us to increase the complexity of the systems studied. We have extended our previous work in two ways, first by modelling the interaction of water with more complex materials such as magnesium silicate and iron oxide and secondly, by considering the initial stages of dissolution by evaluating the energies of replacing the surface cations with protons. We find that there is a strong interaction between the surfaces and water. The bonding of the surface to the water molecules is dominated by the cation–water interactions but is moderated by the area occupied by each water molecule, which is approximately 10 Ų. In addition, as expected, the dissolution energies are highly dependent on cation coordination and the type of cation present, with Ca being energetically more favoured than Mg, and the surface structure as illustrated by Fe₂O₃.