In this thesis we present the results of our simulation studies of iron sulphide minerals, with focus on bulk, surface and cluster chemistry. DFT+U calculations were employed to study the mineral greigite (Fe3S4), which has important implications in Origin of Life theories. Using a combination of DFT and Monte Carlo methods, we were able to explore the probable cation distribution of Ni-doped greigite over the two available lattice sites (tetrahedral and octahedral) at varying concentrations, as well as calculate the enthalpy of mixing and thus deduce at what concentration of Ni this mineral would be most stable. Results showed that within the lattice, site occupation by Ni will be concentration-dependent, whilst violarite, FeNi2S4, is likely to be the most stable (Fe,Ni)S phase. The (001), (011), and (111) surfaces of violarite, both naked and in the presence of water, were investigated next, using a combination of DFT-D2+U methods. The (001) was found to be the most stable surface, whilst the (011) the most reactive with respect to water. The adsorption and dissociation of water on the surfaces also revealed a synergistic effect, whereby the adsorption of one water has a conducive effect on the adsorption of the next. CPMD simulations were then conducted on the following hydrated ions: Fe2+, Fe3+ and S2-, and on the following systems, FexSy (x,y≤ 4), to investigate the structural and dynamical properties in water. Calculation of the Gibbs free energies (ΔGaq) revealed that the formation of FexSy clusters with x,y ≤2 will not only be in competition with the formation of iron hydroxides, but is also temperature-dependent.
|Haider, S. G.
|University College London (University of London)
|Electronic Thesis or Dissertation
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