EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The critical point and the supercritical regime of MgO

Tim Bögels1 and Razvan Caracas2,3
Tim Bögels and Razvan Caracas
  • 1CNRS, Laboratoire de Géologie de Lyon, Centre Blaise Pascal, Ecole Normale Supérieure de Lyon, Lyon, France
  • 2The Center for Earth Evolution and Dynamics (CEED), University of Oslo, Oslo, Norway
  • 3Institut de Physique du Globe de Paris, CNRS, Université de Paris, Paris, France

The position of the critical point determines the top of the liquid-vapor coexistence dome, and is a physical parameter of fundamental importance in the study of high-energy shocks, including those associated with large planetary impacts. For most major planetary materials, like oxides and silicates, the estimated position of the critical point is below 1 g/cm3 at temperatures above 5000 K. Here we compute the position of the critical point of one of the most ubiquitous materials: MgO. For this, we perform first-principles molecular dynamics simulations. We find the critical density to be in the 0.4 - 0.6 g/cm3 range and the critical temperature in the 6500 - 7000 K range. We investigate in detail the behavior of MgO in the subcritical and supercritical regimes and provide insight into the structure and chemical speciation. We see a change in Mg-O speciation towards lower degrees of coordination as the temperature is increased from 4000 K to 10000 K. This change in speciation is less pronounced at higher densities. We observe the liquid-gas separation in nucleating nano-bubbles at densities below the liquid spinodal. The majority of the chemical species forming the incipient gas-phase consist of isolated Mg and O atoms and some MgO and O2 molecules. We find that the ionization state of the atoms in the liquid phase is close to the nominal charge, but it almost vanishes close to the liquid-gas boundary and in the gas phase, which is consequently largely atomic.


This research was supported by the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818–IMPACT to RC). This research was performed by access to supercomputing facilities via eDARI stl2816 grants, PRACE RA4947 grant, Uninet2 NN9697K grant.

How to cite: Bögels, T. and Caracas, R.: The critical point and the supercritical regime of MgO, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5002,, 2022.