Thermodynamic properties of solid and liquid silicates and oxides in the TPa range from ab initio calculations

要改进对太阳系外超级地球内部结构及其通过洛夫数k2可观测到的引力反应的描述-这是研究股的中心目标之一-就需要详细了解压力和温度高达1 TPa和10 000 K时的材料特性。在这里，我们建议进行从头计算的结构，稳定性和热力学性质的硅酸盐和氧化物固体和液体。对于液体，从头算分子动力学模拟将进行的目标是提供能量和压力，以适应熔体的自洽热力学模型-制定为有限应变和降低温度方面的亥姆霍兹能量的泰勒展开-我们以前已经成功地应用于液体铁。在500 GPa附近，MgO经历了从B1到B2结构的相变，实验和模拟之间基本一致。实验表明，FeO在高温下经历相同的转变，但这种转变在模拟中仍然难以捉摸。在这里，我们建议探索在高温下这些阶段的稳定性的非谐声子贡献的影响，使用随机自洽谐波晶格动力学（SSCHA）的方法。根据结果，我们将进一步尝试探索这种过渡沿着的MgO-FeO固溶体与集群expansion approach.Previous结果的声子分散在硅酸盐固体在超地球内部的条件下，从第一个资金周期将进一步探讨剪切模量，这提供了一个重要的约束勒夫数k2的行星的引力响应。

An improved description of the internal structure of extrasolar super-Earths and their observable gravitational response through the Love number k2 -- which is one of the central goals of the Research Unit -- requires a detailed knowledge of material properties at pressures and temperatures up to 1 TPa and 10,000 K. Here we propose to perform ab initio computations on the structure, stability and thermodynamic properties of silicate and oxide solids and liquids. For the liquids, ab initio molecular dynamics simulations will be performed with the goal to provide energies and pressures to fit a self-consistent thermodynamic model for the melts -- formulated as a Taylor expansion of Helmholtz energy in terms of finite strain and a reduced temperature -- that we previously have successfully applied to liquid Fe. In the vicinity of 500 GPa, MgO undergoes a phase transition from the B1 to the B2 structure, in general agreement between experiments and simulations. Experiments indicate that FeO undergoes the same transition at high temperature, but this transition has remained elusive in simulations to this point. Here we propose to explore the influence of anharmonic phonon contributions on the stability of these phases at high temperature, using the stochastic self-consistent harmonic lattice dynamics (SSCHA) approach. Depending on the results, we will further attempt to explore this transition along the MgO-FeO solid solution with the cluster expansion approach.Previous results for the phonon dispersion in silicate solids at conditions of super-Earth interiors from the first funding period will be further explored in terms of the shear modulus, which provides an important constraint on the Love number k2 for a planet's gravitational response.