Ab initio reaction networks of carbon dioxide in supercritical water: bulk and nanoconfinement studies Chu Li 1 , Yuan Yao 3 , Ding Pan 1,2 1 Department of Physics, The Hong Kong University of Science and Technology, China, 2 Department of Chemistry, The Hong Kong University of Science and Technology, China, 3 Department of Mathematics, The Hong Kong University of Science and Technology, China Understanding the reactions of aqueous carbon at extreme pressure and temperature conditions is of great importance to the carbon transport in the deep Earth, but it is very challenging to conduct experimental investigations at the molecular scale. Ab initio molecular dynamics (AIMD) is a powerful computational tool for simulating molecular reactions without experimental input. However, its computational demands often limit the timescale of the simulations. To overcome this limitation, we constructed Markov State Models (MSMs) based on AIMD simulations to study the reaction kinetics of carbon dioxide (CO 2 ) in supercritical water. Our MSMs revealed distinct reaction networks for CO 2 −H 2 O reactions in bulk water and under graphene nanoconfinement. Specifically, we observed two contrasting reaction pathways leading to the formation of carbonate or bicarbonate ions. We also found that the reaction CO 2 (aq)+H 2 O→HCO 3 - +H + is often facilitated by rapid proton transfers along hydrogen-bonded water wires. These transfers occurred in a concerted manner in bulk water but stepwise under nanoconfinement. Our work provides an unbiased and systematic approach to constructing chemical reaction networks using AIMD trajectories, offering molecular insights into CO 2 behavior in supercritical water. The results of this study have significant implications for the deep carbon cycle.
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© The Author(s), 2023
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