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DFT Simulations of the Structure and Cation Order of Norsethite, BaMg(CO3)2

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journal contribution
posted on 25.05.2021, 18:37 by Carlos Pimentel, Carlos M. Pina, C. Ignacio Sainz-Díaz
Norsethite, BaMg­(CO3)2, is an interesting mineral that can be used to investigate processes leading to the formation of dolomite and other dolomite-type structures. To this end, it is first necessary to study in detail the Ba–Mg cation arrangement in the crystal structure of norsethite. In this work, first-principles calculations based on density functional theory (DFT) have been used to simulate cation ordering for the crystal structures of two BaMg­(CO3)2 polymorphs: the low-temperature polymorph (up to ∼360 K), α-norsethite (Rc), and the high-temperature polymorph (above ∼360 K), β-norsethite (Rm). We found that for both structural variants of norsethite, the most stable cation arrangements are those with the alternation of barium and magnesium layers along the c-axis. Furthermore, we have adequately simulated nonstoichiometric β-norsethite structures since some synthetic norsethites were found to have an excess of magnesium, which seems to favor the crystallization of β-norsethite at room temperature.