Pressure-Induced Magnetic Collapse and Metallization of Molecular Oxygen: Theζ-O2Phase

The behavior of solid oxygen in the pressure range between 5–116 GPa studied with ab initio simulations, shows a spontaneous phase transformation from the antiferromagnetic insulating $\delta$- ${\mathrm{O}}_2$ phase to a nonmagnetic, metallic molecular phase. The calculated static structure factor of this phase is in excellent agreement with x-ray diffraction data in the metallic $\zeta$- ${\mathrm{O}}_2$ phase above 96 GPa. We thus propose that $\zeta$- ${\mathrm{O}}_2$ should be base centered monoclinic with space group $C2\mathrm{}/m$ and four molecules per cell, suggesting a reindexing of the experimental diffraction peaks. Physical constraints on the intermediate-pressure $\epsilon$- ${\mathrm{O}}_2$ phase are also obtained.