Abstract
Ab initio random structure searching (AIRSS) and density functional theory methods are used to predict structures of calcium and magnesium carbonate and at high pressures. We find a previously unknown structure which is more stable than the aragonite and “post aragonite” phases in the range 32–48 GPa. At pressures from 76 GPa to well over 100 GPa the most stable phase is a previously unknown structure of the pyroxene type with fourfold coordinated carbon atoms. We also predict a stable structure of in the range 85–101 GPa. Our results lead to a revision of the phase diagram of over more than half the pressure range encountered within the Earth's mantle, and smaller changes to the phase diagram of . We predict to be more stable than in the Earth's mantle above 100 GPa, and that is not a thermodynamically stable compound under deep mantle conditions. Our results have significant implications for understanding the Earth's deep carbon cycle.
1 More- Received 15 November 2013
- Revised 29 April 2014
DOI:https://doi.org/10.1103/PhysRevB.91.104101
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