Stable Xenon Nitride at High Pressures

Nitrogen is the most abundant element on Earth and exists as inert N$_{2}$ molecules in the atmosphere. Noble gas nitrides are missing in nature because N$_{2}$ molecules do not interact with noble gases at ambient conditions, greatly impeding the understanding of physics and chemistry of such nitrides. We report here a pressure-induced chemical reaction of N$_{2}$ with xenon predicted using a swarm-structure searching calculation as implemented in the CALYPSO code [1-2]. This reaction leads to the formation of a hitherto unexpected Xe nitride at megabar pressure accessible to high-pressure experiments. The high-pressure phase with a hypervalent state of Xe by accepting unprecedented Xe-N covalent bonds appears to be the most stable stoichiometry. The Xe bonding situation in this new phase is substantially different from earlier high-pressure examples of ionic Xe bonding or van der Waals interactions. \\[4pt] [1] Wang, Y., Lv, J., Zhu, L. {\&} Ma, Y. Crystal structure prediction via particle-swarm optimization. Phys. Rev. B 82, 094116 (2010).\\[0pt] [2] Wang, Y., Lv, J., Zhu, L. {\&} Ma, Y. CALYPSO: A method for crystal structure prediction. Comput. Phys. Commun. 183, 2063--2070 (2012).