Exploring KNO3 behaviour and Formation through Simulation

Alkali metal nitrates are both of industrial and scientific interest. In this thesis, we present a new rigid-ion force-field for the alkali metal nitrates that is suitable for simulating solution chemistry, crystallisation and polymorphism. We show that it gives a good representation of the crystal structures, lattice energies, elastic and dielectric properties of these compounds over a wide range of temperatures. Since all the alkali metal nitrates are fitted together using a common model for the nitrate anion, the force-field is also suitable for simulating solid solutions. We utilise our model by exploring, in particular, KNO3 behaviour in a range of systems. Because the ultimate goal is to model the nucleation, and subsequent crystallisation, of KNO3 we have explored a few possible scenarios, from an homogeneous to an heterogeneous one. We have started by attempting to nucleate KNO3 from pure, supersaturated solutions. Because of the statistically rare nature of the event, we tried to make the process possible to investigate in a time frame that is also optimal for simulation, by putting said solutions in contact with a slab of KNO3. We add a constant chemical potential method (Cμ-MD) to our model to try to determine growth mechanisms and rates. At this stage of this work no clear growth behaviour has been observed. We then swapped the slab of KNO3 for a self-assembled monolayer (SAM) surface to investigate the effect of functional groups, charges and defects on the nucleation process. In this case, the results were not comparable with the ones obtained for CaCO3 because the nucleation was not significantly accelerated by the presence of the defects.