从第一性原理看水化和磁性在水铁矿结构中的作用,ACS Earth and Space Chemistry

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从第一性原理看水化和磁性在水铁矿结构中的作用
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2018-11-19 00:00:00 , DOI: 10.1021/acsearthspacechem.8b00138
Michel Sassi ₁ , Kevin M. Rosso ₁

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我们报告了密度泛函理论计算，旨在预测由结构水的量决定的一系列可能组成中的水铁矿的热力学稳定结构。基于假设的Fe ₅ O ₈ H + n H ₂ O的公式单位，我们进行了从头算的进化搜索，以求出最低焓焓结构，该焓函数是水含量直至n的函数。=2。这是迄今为止进行的水铁矿结构的最详尽的搜索。生成了超过5000种独特的配置，并评估了五种水合作用状态。其中，生成了Michel akdaliate模型，以及在较高水合作用状态下具有能量上可比的新结构。但是，对50个最低能量结构的计算对和分布对分布函数与X射线衍射图进行直接比较，结果表明，除了Michel模型之外，没有其他元素与水铁矿有关。尽管如此，这种在能量上可比的结构集为分析和理解水合和磁性对水铁矿拓扑的影响提供了新的基础，由此我们得出结论，任何四面体铁都应被视为亚稳态结构缺陷，

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Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles

We report density functional theory calculations aimed at predicting thermodynamically stable structures for ferrihydrite across a range of possible compositions determined by the amount of structural water. Based on an assumed formula unit of Fe₅O₈H + nH₂O, we performed ab initio calculations with evolutionary searching to find the lowest enthalpy structures as a function of the water content up to n = 2. This is the most exhaustive search for the ferrihydrite structure conducted so far; more than 5000 unique configurations were generated and evaluated over five states of hydration. Among them, the Michel akdaliate model was generated, along with several energetically comparable new structures at higher states of hydration. However, a direct comparison between calculated and experimental pair distribution function and X-ray diffraction patterns for the 50 lowest energy structures shows that none beyond the Michel model could be associated with ferrihydrite. Nevertheless, this energetically comparable structure set provides a novel basis for analyzing and understanding the effects of hydration and magnetism on the topology of ferrihydrite, from which we conclude that any tetrahedral Fe should be viewed as a metastable structural defect, created either as a result of the rapid kinetics of crystal growth or to accommodate a local magnetic stress between neighboring Fe atoms.

更新日期：2018-11-19

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