The structure and electronic properties of aqueous fluids at the mineral/surface interface influence many chemical processes such as mineral growth and dissolution, natural oxidation-reduction reactions and biochemical respiration. The metal oxide minerals that are key to these processes present a difficult electronic structure problem since their properties are heavily dependent on the properties of strongly localized d electrons. The disorder of the surface/solution interface, the interaction of the solution phase with the highly charged mineral surface, and the need to dynamically sample the structure of the interface phase further increases the computational complexity. We have developed computational methods that are designed to treat these problems. Highly parallel gradient corrected DFT calculations have been used to calculate surface structure and the reactions of mineral surfaces with absorbed layers containing reactive solutes. These calculations, done using many processors, can describe limited (10s of ps) interface dynamics. To obtain even qualitative agreement with the spin localization in these systems it is necessary to include some level of exchange. We have developed highly parallel algorithms that implement hybrid exchange functionals. This code is computationally still too demanding for very large systems so we have developed DFT + U software that is efficient enough for dynamical simulations and gives qualitatively similar results to the hybrid PBE0 correction. For even higher levels of approximation we have developed novel parallel in time algorithms. These methods compute the time dimension of a dynamical simulation in a parallel fashion and can efficiently spread high level electronic structure methods over many processors. Various sampling methods have been used to try to overcome the structural complexity of the problem.We have tested our computational methods against experimental data. EXAFS observations of highly charged ions in solution are reproduced with remarkable accuracy. They both allow us to validate the levels of approximation of the electronic structure calculation and provide a new level of parameter free interpretation of the data. Similar efforts to describe XRD data from interfaces will be presented.

First principles simulation of mineral/fluid interactions: Methods development, application to metal oxide interfaces, and analysis of observations

248th National Meeting (2014)

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