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Ab initio study of the structure and stability of CaMg(CO_3)_2 at high pressure

Solomatova, Natalia V. and Asimow, Paul D. (2017) Ab initio study of the structure and stability of CaMg(CO_3)_2 at high pressure. American Mineralogist, 102 (1). pp. 210-215. ISSN 0003-004X.

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Dolomite is one of the major mineral forms in which carbon is subducted into the Earth’s mantle. End-member CaMg(CO_3)_2 dolomite typically breaks down upon compression into two carbonates at 5–6 GPa in the temperature range of 800–1200 K (Shirasaka et al. 2002). However, high-pressure X-ray diffraction experiments have shown that dense high-pressure polymorphs of dolomite may be favored over single-cation carbonates (Santillán et al. 2003; Mao et al. 2011; Merlini et al. 2012). Here we compare calculated dolomite structures to experimentally observed phases. Using density functional theory interfaced with a genetic algorithm that predicts crystal structures (USPEX), a monoclinic phase with space group C2/c was found to have lower energy at pressures above 15 GPa than all previously reported dolomite structures. It is possible that this phase is not observed experimentally due to a large activation energy of transition from dolomite I, resulting in the observed second-order phase transition to a metastable dolomite II. Due to the complex energy landscape for candidate high-pressure dolomite structures, several structurally unique metastable polymorphs exist. We calculate the equation of state of a set of lowest-energy dolomite polymorphs with space groups P1, P2/c, and C2/c up to 80 GPa. Our results demonstrate a need for calculations and experiments on Fe-Mn bearing high-pressure carbonate phases to extend our understanding of Earth’s deep carbon cycle and test whether high-pressure polymorphs of double-cation carbonates represent the main reservoir for carbon storage within downwelling regions of Earth’s mantle.

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Solomatova, Natalia V.0000-0002-2331-3427
Asimow, Paul D.0000-0001-6025-8925
Alternate Title:Ab initio study of the structure and stability of CaMg(CO3)2 at high pressure
Additional Information:© 2017 Mineralogical Society of America. Manuscript received April 26, 2016; Manuscript accepted August 24, 2016; Manuscript handled by Martin Kunz. We thank E.A. Schauble, A. Kavner, M. Merlini, G.F. Finkelstein, A.R. Oganov, and O. Hellman for valuable discussions and insights. We are thankful to N. Near-Ansari for assistance with technical aspects using FRAM, the high-performance computing cluster at Caltech. This work is supported by the U.S. National Science Foundation through award EAR-1551433.
Funding AgencyGrant Number
Subject Keywords:Dolomite, ab initio, global carbon cycle, lower mantle, high pressure
Issue or Number:1
Record Number:CaltechAUTHORS:20170112-124637100
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Official Citation:Ab initio study of the structure and stability of CaMg(CO3)2 at high pressure Natalia V. Solomatova, Paul D. Asimow American Mineralogist Jan 2017, 102 (1) 210-215; DOI: 10.2138/am-2017-5830
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73476
Deposited By: Tony Diaz
Deposited On:20 Jan 2017 00:05
Last Modified:03 Oct 2019 16:28

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