A novel MgHe compound under high pressure

Helium, with a full-shell electronic structure, is the most inert element in the periodic table at atmospheric pressure. The study of the reaction between helium and other non-noble-gas elements as well as relevant compounds has attracted great attention in the fields of chemistry, physics, materials and planetary science. In this study, we found a stable compound of MgHe with P6₃/mmc symmetry at pressures above 795 GPa within zero-point energy. Thermodynamic stability calculations of P6₃/mmc phase at high temperatures and pressures indicate that this structure may exist in the interior of the super-Earth and Neptune. Our further simulations on the electron localization function and Bader analysis show that the predicted compound is an electride with −1.093e in the quantized interstitial quasiatom (ISQ) orbitals, which are localized at interstitial sites in the crystal lattice. Our study provides a theoretical basis for studying the physical and chemical properties of MgHe and the existence of MgHe in gaseous planets.