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

• Applicant: Dr. Gerd Steinle-Neumann
• Subject Area: Geophysics ; Mineralogy, Petrology and Geochemistry ; Theoretical Condensed Matter Physics
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 280637173

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.

• DFG Programme: Research Units
• Subproject of: FOR 2440: Matter Under Planetary Interior Conditions - High-Pressure, Planetary and Plasma Physics
• Co-Investigator: Professor Dr. Ronald Redmer