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 (R3̅c), and the high-temperature polymorph (above ∼360 K), β-norsethite (R3̅m). 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.

中文翻译：

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Norsethite, BaMg(CO ₃ ) ₂的结构和阳离子顺序的 DFT 模拟

Norsethite BaMg(CO ₃ ) ₂是一种有趣的矿物，可用于研究导致白云岩和其他白云岩型结构形成的过程。为此，首先需要详细研究雪铁矿晶体结构中的 Ba-Mg 阳离子排列。在这项工作中，基于密度泛函理论 (DFT) 的第一性原理计算已被用于模拟两种 BaMg(CO ₃ ) ₂多晶型的晶体结构的阳离子排序：低温多晶型（高达 ~360 K）， α-norsethite ( R 3̅ c )，以及高温多晶型物（高于 ~360 K），β-norsethite ( R 3̅ m）。我们发现，对于 Norsethite 的两种结构变体，最稳定的阳离子排列是沿c轴交替排列的钡和镁层。此外，我们已经充分模拟了非化学计量的 β-norsethite 结构，因为发现一些合成的norsethite 含有过量的镁，这似乎有利于 β-norsethite 在室温下结晶。