Elucidation of Bottom-Up Growth of CaCO3 Involving Prenucleation Clusters from Structure Predictions and Decomposition of Globally Optimized (CaCO3)n Nanoclusters.

Low-energy minima structures for (CaCO3)n, n 20 formula units are surface stabilized with negative surface energy densities. In contrast, the top-down cluster are interior stabilized with positive surface energy densities. We prove that the sign of the surface energy density determines whether the nucleation reaction energy as a function of nuclear size has a maximum or a minimum. The surface-stabilized bottom-up clusters are proposed to be a type of prenucleation cluster at the minimum of the nucleation reaction energy. A mechanism for mineralization of CaCO3 involving prenucleation clusters and non-classical growth pathway is proposed on the basis of our theoretical findings, which is consistent with previous titration experiments.