Reactivity of Noble Gases under High Pressure

There has been recently a trend in finding how high pressure can enable the reactivity of noble gases (NG). The discovery of Xe oxidation meant a doctrinal change, by showing that a complete electron shell is not inert to reaction. However reduced NG atoms in chemical compounds were not found, neither experimentally nor theoretically. Using first-principles electronic structure calculations coupled with a structure prediction method, we have found that Xe, Kr, and Ar can form thermodynamically stable compounds with Mg at high pressure ($\geq 125$, $\geq 250$, and $\geq 250$ GPa, respectively). The compounds are metallic and the NG atoms are negatively charged, suggesting that chemical species with a completely filled shell become reduced. Moreover, Mg$_2$NG are high-pressure electrides. Inspired by recent research,\footnote{\tt arXiv:1309.3827 [cond-mat.mtrl-sci]} we extended the study to the mixtures of different compounds of Mg, Li and N with He. We performed a systematic structure search from $10^{-4}$ to $300$ GPa for mixtures with different ratios of He.