EAPSI: Evaluating the Melting and Vibrational Properties of Phase H as a Function of Pressure

四十年来有关这一主题的科学文献对地球深处的水含量做出了千差万别的估计--其值从地球海洋中发现的水量的四分之一到四倍不等。最近发现的含水“H相”(MgSiO4H2)为了解地球内部水的分布提供了新的见解。确定H相等含水相的稳定性有助于限制下地幔中的水的数量，而下地幔是地球上一个质量几乎是地壳100倍的区域。H相的形成最初是由日本爱慕大学地球动力学研究中心(GRC)的土屋纯博士进行的一项计算研究预测的。土屋博士将利用第一性原理技术为这个项目提供研究高压水合相的专业知识，GRC将提供一台超级计算机，使这个项目能够及时完成。这项提议旨在通过对关键的含水地幔相的三个从头算研究，提供对地球深层氢收支的重要洞察：(1)模拟H相的熔融行为作为压力的函数，(2)模拟d-AlOOH的熔化曲线，以及(3)第一性原理计算H相的振动性质作为压力的函数。用第一性原理分子动力学技术测定了H相和d-AlOOH相的熔融曲线。这种类型的计算能够通过对感兴趣的系统中的粒子之间的原子间势进行数值建模来确定热力学性质。H相的振动性质将使用基于交换关联泛函的广义梯度近似的第一性原理计算。这些计算是对首席研究员S在极端条件下研究含水相的实验努力的补充，将有助于限制地球深部的水资源预算。东亚和太平洋夏季学院计划下的这个奖项支持一名美国研究生的夏季研究，由美国国家科学基金会和日本科学促进会共同资助。

Forty years of scientific literature on the topic has produced wildly variable estimates of the water content within the deep Earth--with values ranging from a quarter to four times the volume of water found in Earth's oceans. The recent discovery of hydrous 'phase H' (MgSiO4H2) provides a new insight into the distribution of water in the Earth's interior. Determining the stability of hydrous phases such as phase H aids in constraining the quantity of water in the lower mantle, a region of the Earth almost 100 times more massive than the crust. The formation of phase H was first predicted in a computational study by Dr. Jun Tsuchiya of the Geodynamics Research Center (GRC) at the University of Ehime, Japan. Dr. Tsuchiya will lend her expertise using first-principles techniques to study high-pressure hydrous phases to this project and the GRC will provide use of a supercomputer that will enable the timely completion of this project.This proposal aims to provide critical insight into the deep Earth's hydrogen budget via three ab initio investigations into key hydrous mantle phases: (1) modeling the melting behavior of phase H as a function of pressure, (2) modeling the melting curve of d-AlOOH, and (3) first-principles calculations of the vibrational properties of phase H as a function of pressure. The melting curves of phase H and d-AlOOH will be determined using a first principles molecular dynamics technique. This type of calculation enables the determination of thermodynamic properties by numerically modeling the interatomic potentials between particles in the system of interest. Vibrational properties of phase H will be calculated using first-principles calculations based on a generalized gradient approximation to the exchange-correlation functional. These calculations are complementary to the principal investigator?s experimental efforts to investigate hydrous phases under extreme conditions and will help constrain the water budget of the Earth's deep interior.This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Japan Society for the Promotion of Science.