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

• Published in: ACS nano Vol. 14; no. 4; pp. 4153 - 4165
• Main Authors: Chen, Mingyang, McNeill, Ashley S, Hu, Yiqin, Dixon, David A
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.04.2020
• Subjects: structure−property relationship; nucleation; calcium carbonate; biomineralization; global geometry optimization; prenucleation cluster
• ISSN: 1936-0851; 1936-086X; 1936-086X
• DOI: 10.1021/acsnano.9b08907

Low-energy minima structures for (CaCO3) n , n ≤ 28, are predicted using bottom-up genetic algorithms in conjunction with density functional theory electronic structure calculations, in comparison with the frozen and relaxed top-down clusters generated by cuts from the calcite, vaterite, and aragonite crystal structures. Similarities in structural motifs for the bottom-up and relaxed top-down are revealed using a fragment recognition technique. Fragment energy decomposition analysis shows that the bottom-up and relaxed top-down clusters belong to two classes of amorphous clusters with distinct intracluster energy distributions, despite their structural similarity. The bottom-up clusters with >20 formula units are surface stabilized with negative surface energy densities. In contrast, the top-down clusters 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 nonclassical growth pathway is proposed on the basis of our theoretical findings, which is consistent with previous titration experiments.