Effects of valence and spin of Fe in MgSiO3 melts: Structural insights from first-principles molecular dynamics simulations
Effects of valence and spin of Fe in MgSiO3 melts: Structural insights from first-principles molecular dynamics simulations
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MgSiO3 熔体中 Fe 价态和自旋的影响：第一性原理分子动力学模拟的结构见解
DOI：
10.1016/j.gca.2020.03.040
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发表时间：
2020
影响因子：
5
通讯作者：
Ghosh, DB and
中科院分区：
文献类型：
--
作者：
Ghosh, DB and
铁（Fe）存在于陆地熔体中，并存在于地球内部的所有深度。铁在其不同的氧化态和自旋态如何影响硅酸盐熔体的性质对于理解我们星球的化学演化至关重要。在这里，我们报告的第一性原理分子动力学模拟结果的熔融铁轴承MgSiO 3在一个广泛的压力范围内覆盖整个地幔。我们的研究结果表明，主机熔体的结构特性，如平均键长和协调的Mg-O和Si-O没有太大的不同时，与纯熔体相比。更重要的是，它们表明局部Fe-O结构对铁的自旋状态（高自旋，HS和低自旋，LS）比其价态（Fe 2+和Fe 3+）更敏感。对于等价构型，HS和LS态之间的平均Fe-O键长和配位数分别相差超过10%和30%。相比之下，Fe 2+和Fe 3+的同位旋组态之间的相应差异分别在5%和15%以内。在0 GPa和3000 K下，亚铁的HS和LS的平均氧配位数分别为3.8和3.3，而三价铁的相应氧配位数分别为4.1和3.7。随着压力的增加，二价铁和三价铁之间的配位间隙关闭HS，但持续LS。我们的非桥接和桥接氧的比例和键断裂/形成事件的速率的分析表明，在其网络形成能力方面的亚铁和三价铁的等效作用。对于MgO-FeO-SiO2熔体，不同氧化态铁的结构行为与实验结果基本一致.不同于其他的铁硅酸盐组合物的实验数据表明，Fe 3+增加和Fe 2+降低熔体的粘度，亚铁和三价铁，由于它们的结构等效性，可能有一个类似的影响深地幔含铁MgSiO 3熔体的动力学行为。
Iron (Fe) is present in terrestrial melts and at all depths inside the Earth. How Fe in its varying oxidation and spin states influences the properties of silicate melts is of critical importance to the understanding of the chemical evolution of our planet. Here, we report the results of first-principles molecular dynamics simulations of molten Fe-bearing MgSiO3over a wide pressure range covering the entire mantle. Our results suggest that the structural properties of the host melt, such as the average bond length and coordination in Mg–O and Si–O do not differ much when compared with the pure melt. More importantly, they show that the local Fe–O structure is more sensitive to the spin state (high-spin, HS and low-spin, LS) of iron than to its valence state (Fe2+and Fe3+). For iso-valence configurations, the average Fe–O bond length and coordination number differ by more than 10% and ∼30%, respectively, between the HS and LS states. In comparison, the corresponding differences between Fe2+and Fe3+for iso-spin configurations are within 5 and 15%, respectively. Ferrous iron shows lower average oxygen coordination numbers of ∼3.8 for HS and ∼3.3 for LS compared to the corresponding numbers of ∼4.1 and ∼3.7 for ferric iron at 0 GPa and 3000 K. As pressure increases, the coordination gap between the ferrous and ferric iron closes for HS but persists for LS. Our analysis of the proportions of non-bridging and bridging oxygens and the rates of bond breaking/formation events suggests an equivalent role of the ferrous and ferric iron in terms of their network forming ability. The predicted structural behavior of iron in its different oxidation states is generally consistent with the experimental inferences for MgO–FeO–SiO2melts. Unlike other ferrosilicate compositions for which the experimental data suggest that Fe3+increases and Fe2+decreases the viscosity of the melt, the ferrous and ferric iron, due to their structural equivalence, are likely to have a similar influence on the dynamical behavior of deep mantle iron-bearing MgSiO3melts.
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影响因子：
3.7
作者：
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通讯作者：
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DOI：
--
发表时间：
1992
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DOI：
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发表时间：
2006
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DOI：
--
发表时间：
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