The calcite-water interface is one of the most studied mineral growth systems given that it is ameanable to study by a variety of experimental techniques including X-ray reflectivity and atomic force microscopy, where the later can provide growth rates for surface features and even achieve atomic resolution under appropriate conditions. Despite this wealth of studies, there still remain open questions as to the molecular pathways by which ions and organic molecules bind to the basal surface and the thermodynamics of individual attachment events. Computer simulation has also been frequently used to examine binding of molecules to the basal surface of calcite, though the majority of studies have stopped short of computing the free energy of adsorption and only considered internal energies based on limited sampling. This is despite the fact that entropy is known to be important.<br/>In this study we will use molecular dynamics simulations based on thermodynamically-calibrated force fields to examine the reactivity of both the acute and obtuse step edges of calcite on the (10-14) surface. Free energy landscapes are computed using well-tempered multiple-walker metadynamics. Due to the slow dynamics of water exchange at the step edges, it is found to be essential to explicitly sample the water coordination environment of the step in order to obtain meaningful, well-converged pathways for ion adsorption. Based on this approach, the initial mechanism of calcite growth will be described, showing that modification of the conventional model of kink site nucleation is required for calcite. In addition, the possible mechanisms of attachment of simple organics to the calcite surface and step edges will also be examined.

Determining the reactivity of steps at the calcite-water interface from computer simulation

256th National Meeting (2018)

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