Molecular Model for Reactive Interactions of Water and Carbon Dioxide

While the mixture of carbon dioxide with water has been a subject of countless experimental and theoretical investigations, explicit molecular models of the system are still limited to either non-reactive classical force fields or small-scale reactive systems studied by ab initio calculations [1]. Practical problems, however, often require simulations over extended time and length scales, such as for the study of dissolution and precipitation of carbonate minerals or of the effects of pH on surface reactions.

In the present study we explore an alternative to ab initio methods provided by a classical bond order-based reactive force field ReaxFF [2], and use it to capture the complex chemistry of aqueous CO₂. Using DFT ab initio methods, we first create a structure-energy database representing carbon dioxide reactions with water leading to the formation of carbonic acid as well as bicarbonate and carbonate ions, and then use the data to optimize ReaxFF parameters. In subsequent simulations, we test the capabilities and limits of the optimized model to reproduce available experimental data, such as the acidity constants of carbonic acid or rate constants for the main CO₂ + H₂O reactions. To describe reactions leading from molecular aqueous CO₂ to calcium carbonate, we also include calcium in our parameter optimization.

1) Nguyen, M. T.; Matus M. H.; Jackson V. E.; Ngan V T.; Rustad J. R.; Dixon D. A. J. Phys. Chem A 2008, 112, 10386.

2) van Duin, A. C. T.; Dasgupta, S.; Lorant, F.; Goddard, W. A. J. Phys. Chem. A 2001,105, 9396.