Molecular scale studies are essential for the prediction of sorption onto minerals such as clays, in particular in the context of the geological disposal of radioactive waste. Classical molecular simulation have already brought significant insights into the microscopic structure, thermodynamics and dynamics of the clay-solution interface. The predictions of such simulations rely on the quality of the model used to represent interactions between atoms. The current state-of-the-art force field for clays, ClayFF, reproduces well many properties. However, it does not account for polarization, which is known to play an important role at solid-liquid interfaces, in particular in influencing chemical specificity of cation sorption. We will show how DFT calculations can be used to parametrize a polarizable force field, using on the one hand a force/dipole-fitting procedure, which provides a high degree of transferability, and on the other hand a systematic derivation using maximally localized Wannier functions. Another key factor controlling the sorption of cations on clay surfaces is the protonation state of the sites present on clay edges, which is difficult to determine experimentally. Here again, ab-initio simulations provide the necessary tool to determine the corresponding pKa. We discuss the case of the sites present on the (010) surface of pyrophyllite and show that the reorganization of the interface (including surface water molecules) plays an important role. Figure 1. <img src='https://acs-archive-assets2.s3.amazonaws.com/240nm/uploads/31748_figure_1.jpg' alt='' />Ref: Tazi et al., Geochimica at Cosmochimica Acta 94, 1 (2012)

Interfacial properties of clay minerals: Surface acidity and polarizable force field parametrization from ab-initio simulations

247th National Meeting (2014)

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