P-T diagram
P-T diagram of different astrophysical objects.

My main topic of research is the study of the physical properties of materials under planetary interiors conditions using numerical simulations. I primarily use ab initio simulations based on density functional theory (DFT) or on path integral Monte Carlo (PIMC), because they enable us to investigate conditions where the Coulomb interactions are dominant and where the quantum and degenerated behavior of the electrons has to be taken into account. The graph on the right shows the typical conditions I investigate and how they are related to different astrophysical objects.

One of my main interest is the properties of mixtures and how they compare to the pure systems. This has many implications for planets in which the different species may not be phase separated.

Recently, I explored the properties of H-He mixtures when heavy elements such as C, N, O, Si, Fe, MgO, SiO2 are dissolved. I showed that to compute accurate equations of state for planetary interiors, it is necessary to properly take into account the interactions between the heavy elements and the H-He plasma. I also explored the effect of the heavy elements on the internal structure and showed that a Jupiter-like planet with a 2% in mass enrichment in oxygen would be colder by 80K in its deep interior.

I studied mixtures of hydrogen and water under conditions that can be found in the envelope of gas or ice giant planets. I studied the equation of state as well as the miscibility properties using a thermodynamic integration technique. I showed that in the interior of giant planets, hydrogen and water are miscible in all proportion. I also computed the diffusion coefficients and the viscosity which are important quantities when one wants to determine the dynamics of the planetary interiors.

During my PhD, I explored the properties of hydrogen and helium and how they compare to the pure systems. Thanks to the DFT calculations, it is possible to explore the transport properties due to the electrons (electrical and thermal conductivity, absorption, reflectivity,…) and I showed that the mixtures has a very strong non-ideal behavior what concerns these transport properties.

In parallel, I collaborate with experimentalists working at high-power laser facilities and performing shock experiments. These experiments enable us to reach extreme conditions close to the ones of interest for planetary interiors. For instance, using the DFT results I was able to show an increase in the reflectivity of hydrogen-helium mixtures at the phase separation. Such a variation should be observable in shock experiments and therefore gives a possible diagnostic for the phase separation. I also contributed to re-investigate some experimental analysis using DFT predictions to better constrain the pressure ionization of helium.