Potential existence of Xe₃CO₂ compounds with distinct Xe-C covalent bonds under pressures of Earth's core

Abstract

Noble gas compounds have attracted significant research attention, mainly due to their intriguing chemical behavior under high-pressure conditions. In this paper, we identify a compound, C2/m-Xe3CO2, through a synergistic approach combining a particle-swarm optimization empowered structure search and first-principles calculations within a wide pressure range of 200-400 GPa, covering the pressure range of Earth's core. This compound features layered Xe6C2O4 sublattices, showing distinct covalent Xe-C bonds, supported by the calculated electron localization function. The presence of the covalent bonds is further corroborated by the large value of the integrated crystal orbital Hamilton population (-4.02 eV/pair) and the large negative Laplacian (-4.65e/Å5). This leads to an unusual sp3-like hybridization in carbon, involving two oxygen atoms, one carbon atom, and one xenon atom. Additionally, two-phase method molecular dynamics simulations suggest that the compound exhibits liquid-state behavior at 200 GPa and 5000 K above the geotherm of the Earth's core. This shows a potential role for the compound in the liquid phase as a reservoir for the "missing Xe"phenomenon. Our findings not only enhance the understanding of bonding behavior in noble gas compounds, but also suggest the potential presence of Xe3CO2 in various astronomical objects.