Oral: Density Functional Tight Binding Simulation of MgO and Mg(OH)₂ Hydration and Carbonation Process

Density functional tight-binding (DFTB) is a quantum mechanical method for simulating materials and molecular systems. It can be derived from density functional theory (DFT) by Taylor expanding the total energy about a reference charge density. When compared to DFT, DFTB has the advantage of much higher computational efficiency; and when compared to classical molecular dynamics, it has the advantage of providing the electronic structure of the system as well.

DFTB calculations, however, require a number of fitted parameters including hopping and overlap integrals, on-site energies and Hubbard U values, which generally need to be determined for each system of interest. Furthermore, there is a lack of suitable DFTB parameters for the hydration and carbonation processes of magnesium compounds, which are crucial for understanding magnesium corrosion.

In this work we have determined DFTB parameters for magnesium oxide and brucite (magnesium hydroxide). We have used this model to study the interaction of CO₂ and H₂O on the (0001) and (1 0 -1 1) surfaces of brucite, and the (001) surface of MgO. This work provides new insights into the interaction of CO₂ and H₂O on these surfaces, in particular the near-surface bulk water behaviour. Additionally, our parameterisation fills a gap in DFTB simulation of magnesium compounds that will be useful to other researchers.