Conducting MgO liquid and planetary dynamos

We use ab-initio molecular dynamics simulations and Kubo-Greenwood linear response theory to show that liquid MgO becomes electrically conductive and exhibits semimetallic behavior under the extreme conditions of planetary interiors. We find that the electrical and thermal conductivity exceed 10,000 S/m and 100 W/m/K, respectively, at pressures (10²-10³ GPa) and temperatures (10³-10⁴ K) characteristic of super-Earth mantles. Both conductivities increase with temperature and pressure, while the Lorenz number and Seebeck coefficient decrease toward values typical of metals. Our calculations of optical reflectivity agree with laser-driven shock experiments. To explain these trends, we analyze the electronic density of states and liquid structure. Finally, as liquid MgO is representative of planetary magma oceans, we discuss the implications of these results on planetary magnetic field generation.