Subproject 1: Thermodynamic properties of silicate solids and liquids and iron to the TPa range from ab-initio calculations
PI: G. Steinle-Neumann, PhD: F. Trybel
An improved description of the internal structure of exosolar super-Earths – which is one of the central goals of the Research Unit – requires a detailed knowledge of material properties at pressures and temperatures that significantly exceed those in the Earths interior, beyond 1 TPa and 10,000 K. Here we propose to investigate – by means of computational techniques – the structure and thermodynamic properties of three material types that are of central importance in planetary structure: (i) silicate and oxide solids, (ii) silicate melts, and (iii) liquid iron.
For the liquids, ab-initio molecular dynamics simulations will be performed with two goals:
- Provide energies and pressures to fit a self-consistent thermodynamic model for liquids. The model is based on an expansion of Helmholtz energy in terms of temperature and finite Eulerian strain following previous work, and can be equally applied to silicate and metallic melts. The thermodynamic model for iron, in particular, will be useful in tightening constraints on the internal structure of cores in super-Earths (SP4).
- To investigate possible phase separation in the silicate liquids. Here, the time-dependent mean-spare displacement and the evolution of the radial distribution functions from the molecular dynamics are analyzed to track the structure of melt components.
High pressure mineral phases beyond post-perovskite have been previously identified in ab-initio computations, and here we plan to follow up on investigating the stability and thermodynamic properties of these phases, using the self-consistent ab-initio lattice dynamics technique. As this method accounts for phonon-phonon interactions, it can stabilize phases that only occur at high temperatures and provides access to Helmholtz energy. Fitting the results to a Birch-Murnaghan Mie-Debye-Gr¨uneisen thermodynamic model for solids – again thermodynamically self-consistent – will provide an avenue to look in detail at phase stability, transition pressures and Clapeyron slopes. These results will be useful in the Research Unit for guiding and interpreting experiments (SP7 and SP8) and model results can be directly used in planetary structure models (SP4).
Ph.D. Gerd Steinle-Neumann
Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth
T: +49 (0)921 55 3702 , Email