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首页> 外文期刊>Physics of the Earth and Planetary Interiors: A Journal Devoted to Obsevational and Experimerntal Studies of the Chemistry and Physics of Planetary Interiors and Their Theoretical Interpretation >A computational study of magnesium point defects and diffusion in forsterite
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A computational study of magnesium point defects and diffusion in forsterite

机译：镁橄榄石中镁点缺陷及其扩散的计算研究

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摘要

We have studied the formation and migration of point defects within the magnesium sub-lattice in forsterite using a combination of empirical and quantum mechanical modelling methodologies. Empirical models based on a parameterised force field coupled to a high throughput grid computing infrastructure allow rapid evaluation of a very large number of possible defect configurations. An embedded cluster approach reveals more accurate estimates of defect energetics for the most important defect configurations. Considering all defects in their minimum energy, equilibrium positions, we find that the lowest energy intrinsic defect is the magnesium Frenkel type, where a magnesium atom moves from the M1 site to form a split interstitial defect. This defect has 2 four-co-ordinated magnesium atoms located outside opposite triangular faces of an otherwise vacant M1 octahedron. The split interstitial defect is more stable than regular interstitials where magnesium is located in either of the two structurally vacant octahedral sites in the hexagonally close packed oxygen lattice. M1 vacancies are also found to form when iron(II) oxidises to iron(III). The energy of the defects away from the equilibrium positions allows the energy barrier to diffusion to be calculated. We have considered the migration of both magnesium vacancies and interstitials and find that vacancies are more mobile. When the contribution from the formation energy of the defects is included we arrive at activation energies for vacancy diffusion that are in agreement with experiment.
机译：我们结合经验和量子力学建模方法研究了镁橄榄石镁亚晶格内点缺陷的形成和迁移。基于与高吞吐量网格计算基础结构耦合的参数化力场的经验模型，可以快速评估大量可能的缺陷配置。嵌入式群集方法揭示了最重要缺陷配置的更准确的缺陷能量学估计。考虑到所有缺陷的最低能量平衡位置，我们发现最低能量本征缺陷为镁弗伦克尔型，其中镁原子从M1位置移动形成分裂的间隙缺陷。此缺陷具有2个四配位的镁原子，它们位于否则为空的M1八面体的相对三角面之外。分裂的间隙缺陷比常规的间隙更稳定，在这种间隙中，镁位于六角形紧密堆积的氧晶格中两个结构上空的八面体位置中的任何一个中。当铁（II）氧化为铁（III）时，也会形成M1空位。远离平衡位置的缺陷能量允许计算扩散的能垒。我们已经考虑了镁空位和间隙的迁移，发现空位更容易移动。当包括缺陷形成能的贡献时，我们得出空位扩散的活化能与实验一致。

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