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

40年来，关于这一主题的科学文献对地球深处的水含量作出了各种各样的估计，其数值是地球海洋中水量的四分之一到四倍。最近发现的含水“H相”（MgSiO 4 H2）为地球内部水的分布提供了新的见解。确定含水相（如H相）的稳定性有助于限制下地幔中的水量，下地幔是地球的一个区域，其质量几乎是地壳的100倍。日本爱媛大学地球动力学研究中心（GRC）的土屋纯博士在一项计算研究中首次预测了H相的形成。土屋博士将利用她的专业知识，使用第一原理技术研究高压含水相，以这个项目和GRC将提供使用一台超级计算机，使这个项目能够及时完成。这个建议旨在提供关键的洞察地球深部的氢预算通过三个从头研究关键含水地幔阶段：（1）模拟H相的熔化行为作为压力的函数，（2）模拟d-AlOOH的熔化曲线，和（3）第一原理计算H相的振动性质作为压力的函数。相H和d-AlOOH的熔化曲线将使用第一原理分子动力学技术来确定。这种类型的计算使得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相的振动特性将使用基于交换相关泛函的广义梯度近似的第一性原理计算来计算。这些计算是对主要研究者的补充？该奖项是由美国国家科学基金会（NSF）和日本科学促进会（Japan Society for the Promotion of Science）共同资助的，隶属于东亚和太平洋夏季研究所（East Asia and Pacific Summer Institutes）项目，旨在资助一名美国研究生的夏季研究。

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.