Molecular Simulation of acid-induced crystal dissociation

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While molecular simulation techniques for studying crystal nucleation and growth experienced significant progress in the past 10 years, the inverse process of crystal dissociation received much less attention. This particularly holds for the investigation of dissolving solids by the help of acids – which combines several challenges that so far render such processes elusive to current modelling approaches. On the one hand, the study of proton transfers calls for quantum calculations that limit the accessible time and length scales of the simulation models. However, statistical significance implies extended sampling of large numbers of possible reaction events and sufficiently large simulation models to address rough surfaces, including the formation of notches and the back-propagation of steps during crystal dissociation. The aim of the present proposal is to transfer the Kawska-Zahn method originally formulated for crystal nucleation and growth to the study of the acid-induced dissolving of solids. This shall provide the efficient prediction of suitable protonation sites, quantum/classical modelling of reactive events and efficient sampling of cascades of dissociation trajectories – thus allowing in-depth mechanistic investigations based on dissolving nm-sized layers. Method development shall be accompanied by application to two rather different classes of systems. As demonstrators we wish to explore the dissociation of calcium carbonates, phosphates and molecular crystals in water as functions of pH, as relevant to sanitary cleaning, biomineral shaping and the uptake of pharmaceutical compounds in the intestinal system.