The nucleation and growth of calcium carbonate has attracted considerable interest due to the relevance to crystallisation of everything from biominerals through to industrial scale. While experiment can provide considerable information regarding such processes, computer simulation is a valuable complement since it can offer atomic level insights into the detailed chemistry occuring. In this study, the use of molecular dynamics simulations to extract free energy landscapes, as shown illustratively in Figure 1, for both the speciation and growth processes of calcium carbonate will be explored, based on both the latest force fields and first principles methods. A particular focus will be the kinetics of water exchange and the thermodynamics of ion attachment at the acute and obtuse steps on the basal plane of calcite. For this system there are range of distinct water binding sites that exhibit rates of exchange that span several orders of magnitude. In order to accurately map the free energy landscape it is essential to allow for the slow dynamics at such sites, which requires simulations that sample of the order of a microsecond. Based such runs it is possible to obtain the individual free energies of binding of ions in the vicinity of both step edges, as well as to probe the mode of binding for ion pairs. These results will be discussed in the light of experimental observations of the differing growth rates for calcite steps.

Computer simulation of the speciation and growth of calcium carbonate

251st National Meeting (2016)

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