Organisation and aggregation of calcium carbonate ions in water via molecular simulation
Abstract
Crystallisation of calcium carbonate (CaCO3) in aqueous solutions is essential for carbon dioxide sequestration and the sustainable production of calcium carbonate materials, which are widely used in industry and increasingly explored for novel applications. While crystallisation is often analysed within the framework of classical nucleation theory, CaCO3 and other ionic crystals often form through amorphous precursor phases, motivating the need for alternative descriptions. In this work, we investigate the relationship between the formation of the first CaCO3 coordination sphere, a fundamental unit of local ordering, and ionic aggregation using two complementary simulation approaches: on-the-fly probability-enhanced sampling (OPES) and asynchronous and infinite-swap replica exchange transition interface sampling (∞RETIS). OPES was used to explore free-energy landscapes, whereas ∞RETIS was used to determine reaction kinetics. We studied systems at two levels of supersaturation, between which the formation of the first coordination sphere exhibited distinct kinetic behaviour. These differences were found to be linked to concentration-dependent ionic aggregation. At lower concentration, aggregation remains limited, whereas higher concentration promotes extensive spinodal-like aggregation. For both concentrations, the first coordination sphere forms within the pre-formed clusters through one of two distinct pathways: either within a cluster close to the minimum size required for its formation, or within larger amorphous aggregates whose size and structure depend on concentration. The coexistence of these pathways at both levels of supersaturation reveals the multifaceted nature of early-stage CaCO3 crystallisation and highlights the importance of differentiating ionic aggregation and organisation.
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BibTeX
@misc{sidler2026organisation,
title = {{Organisation and aggregation of calcium carbonate ions in water via molecular simulation}},
author = {Elizaveta Sidler and Rita S Dias and Raffaela Cabriolu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.18128},
eprint = {2610.18128},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.18128},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Organisation and aggregation of calcium carbonate ions in water via molecular simulation
AU - Elizaveta Sidler
AU - Rita S Dias
AU - Raffaela Cabriolu
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.18128
UR - https://arxiv.org/abs/2610.18128
AB - Crystallisation of calcium carbonate (CaCO_3) in aqueous solutions is essential for carbon dioxide sequestration and the sustainable production of calcium carbonate materials, which are widely used in industry and increasingly explored for novel applications. While crystallisation is often analysed within the framework of classical nucleation theory, CaCO_3 and other ionic crystals often form through amorphous precursor phases, motivating the need for alternative descriptions. In this work, we investigate the relationship between the formation of the first CaCO_3 coordination sphere, a fundamental unit of local ordering, and ionic aggregation using two complementary simulation approaches: on-the-fly probability-enhanced sampling (OPES) and asynchronous and infinite-swap replica exchange transition interface sampling (∞RETIS). OPES was used to explore free-energy landscapes, whereas ∞RETIS was used to determine reaction kinetics. We studied systems at two levels of supersaturation, between which the formation of the first coordination sphere exhibited distinct kinetic behaviour. These differences were found to be linked to concentration-dependent ionic aggregation. At lower concentration, aggregation remains limited, whereas higher concentration promotes extensive spinodal-like aggregation. For both concentrations, the first coordination sphere forms within the pre-formed clusters through one of two distinct pathways: either within a cluster close to the minimum size required for its formation, or within larger amorphous aggregates whose size and structure depend on concentration. The coexistence of these pathways at both levels of supersaturation reveals the multifaceted nature of early-stage CaCO_3 crystallisation and highlights the importance of differentiating ionic aggregation and organisation.
ER -