Crystal Buoyancy in the Deep Magma Ocean

今天的地球是一个进化过程的产物，这个进化过程始于一个基本上或完全熔化的行星。该项目旨在限制早期岩浆海洋中固体和液体中的铁含量。固体在岩浆中的升沉取决于它们与液体的密度对比，这是它们的相对铁含量的函数。铁在相间的分配称为分配。量化早期岩浆海洋中的铁的分配对于模拟地球向今天的结构和组成的地幔演化至关重要。在这里，研究人员使用计算物理在原子水平上模拟岩浆中铁的化学。这一模拟被称为“从头算”，因为它依赖于量子力学的基本原理，它解释了深部岩浆海洋中普遍存在的极端压力。该团队的最先进的代码包括允许计算铁与固体和液体的亲和力的开发，因此无论矿物是上升还是下降。该项目促进了计算矿物物理研究生的培养。它影响了邻近的实验岩石学和地球动力学领域，对解释现代地球化学和地震学观测具有重要意义。它在材料科学中也有广泛的影响。以前的工作已经表明，晶体在岩浆海洋中升起或沉没，关键取决于铁在液态和晶态之间的分配。然而，在深部岩浆海洋条件下，液晶密度对比度的标志和地球化学演化的矢量是未知的。在这里，皮尔和他的团队从头算出了铁在整个下地幔压力机制中共存相之间的分配。该项目是密度泛函理论在岩浆海洋中应用的一次重大扩展。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。该团队在从头模拟地球含铁系统--包括强关联和磁熵--方面取得的成就的基础上，扩大了范围，以考虑自由能和元素分配。利用第一原理分子动力学和绝热开关，他们将预测铁的分配范围：1)液体和晶体(镁，铁)O，2)液体和晶体(镁，铁)二氧化硅和3)液体接近块状硅酸盐地球组成和(镁，铁)O铁方镁石和(镁，铁)硅桥石。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.