Amorphous calcium carbonate (ACC) is a critical transient phase in the inorganic precipitation of CaCO3 and in bio- and biomimetic mineralization. The CaCO3 system has also been central to the development of new understanding of nucleation from aqueous solutions. Experimental studies of the non-classical crystallization pathway show the formation of energetically stable pre-nucleation clusters (PNCs) of calcium carbonate followed by the formation of hydrous ACC, anhydrous ACC, and finally transforms into the crystalline phases, e.g. calcite, vaterite, and rarely aragonite. We present here the results of computational molecular dynamics (MD) studies of two important stages of the crystallization pathway, (i) the formation of pre-nucleation clusters from aqueous solution of calcium carbonate and, (ii) dehydration of hydrated ACC to anhydrous ACC. The MD simulations show formation of stable PNCs from solution with structures that progressively reorganize as water content decreases. During dehydration, the simulations show that ACC undergoes reorganization to a more ordered structure with a significant increase in density where the density of the final anhydrous ACC is similar to that of calcite. Water molecules play a crucial role in all of these processes via hydrogen bonding interactions with the anions and completion of the nearest neighbor coordination shell around the cations.

Molecular dynamics simulation of amorphous calcium carbonate (ACC)

245th National Meeting (2013)

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