Crystal Buoyancy in the Deep Magma Ocean

今天的地球是一个进化过程的产物，它开始于一个大部分或完全熔融的行星。本项目旨在限定早期岩浆海中固液相铁含量。固体在岩浆中是上升还是下沉，取决于它们与液体的密度对比，这是它们相对铁含量的函数。铁在相之间的分布称为分配。量化早期岩浆海洋中的铁分配对于模拟地球地幔向现今结构和组成的演化至关重要。在这里，研究人员使用计算物理学在原子水平上模拟岩浆中铁的化学反应。这个模拟——被称为“从头开始”，因为它依赖于量子力学的第一原理——解释了深岩浆海洋中普遍存在的极端压力。该团队最先进的代码包括允许计算铁与固体和液体相的亲和力，从而计算矿物是上升还是下沉。本项目促进了计算矿物物理研究生的培养。它影响了相邻的实验岩石学和地球动力学领域，对现代地球化学和地震学观测的解释具有重要意义。它在材料科学领域也有广泛的影响。先前的研究表明，岩浆海中的晶体是上升还是下沉，关键取决于铁在液态和结晶阶段之间的分配。然而，在深部岩浆海条件下，液晶密度对比的标志和地球化学演化的矢量是未知的。在这里，PI和他的团队从头开始计算铁在整个下地幔压力范围内共存相之间的分配。该项目是密度泛函理论应用于岩浆海的一次重大拓展。它包括端元组成和液体与晶体之间的化学相互作用的研究。该团队在从头开始模拟地球含铁系统（包括强相关性和磁熵）方面取得的成就的基础上，扩大了考虑自由能和元素划分的范围。利用第一性原理分子动力学加上绝热开关，他们将预测铁在以下之间的分配：1)液体和结晶（Mg,Fe）O, 2)液体和结晶（Mg,Fe）SiO3和3)近似块状硅酸盐组成的液体和（Mg,Fe）O铁长石和（Mg,Fe）SiO3桥方石。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Present-day Earth is the product of an evolutionary process which began with a largely or completely molten planet. This project aims to constrain the iron contents of solid and liquid phases in the early magma ocean. Whether solids rise or sink in a magma depends on their density contrast with the liquid, which is a function of their relative iron contents. The distribution of iron between phases is called partitioning. Quantifying iron partitioning in the early magma ocean is critical to model Earth's mantle evolution toward its present-day structure and composition. Here, the researcher uses computational physics to model at the atomic level the chemistry of iron in the magma. The simulation - called "ab initio" because it relies on quantum-mechanics first principles - accounts for the extreme pressures prevailing in the deep magma ocean. The team's state-of-the-art code includes developments which allow calculating the affinity of iron with solid and liquid phases, thus whether minerals rise or sink. This project promotes the training of a graduate student in computational Mineral Physics. It impacts the adjacent fields of Experimental Petrology and Geodynamics, with strong implications for the interpretation of modern geochemical and seismological observations. It also has broad impacts in Materials Science. Previous work has shown that whether crystals rise or sink in a magma ocean depends critically on the partitioning of iron between liquid and crystalline phases. Yet, the sign of the liquid-crystal density contrast and the vector of geochemical evolution is unknown at the conditions of the deep magma ocean. Here, the PI and his team calculates ab initio the partitioning of iron among coexisting phases throughout the pressure regime of the lower mantle. The project represents a major expansion for the application of density functional theory to the magma ocean. It encompasses studies of end-member compositions and the chemical interaction between liquids and crystals. The team build on their accomplishments in ab initio simulation of Earth's iron-bearing systems - including strong correlation and magnetic entropy - by broadening the scope to account for free energies and element partitioning. Using first principles molecular dynamics coupled with adiabatic switching, they will predict iron partitioning between: 1) liquid and crystalline (Mg,Fe)O , 2) liquid and crystalline (Mg,Fe)SiO3 and 3) a liquid approximating bulk silicate Earth composition and (Mg,Fe)O ferropericlase and (Mg,Fe)SiO3 bridgmanite.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.