Pressure-induced magnetic collapse and metallization of molecular oxygen:: The ζ-O2 phase

The behavior of solid oxygen in the pressure range between 5-116 GPa studied with nb initio simulations, shows a spontaneous phase transformation from the antiferromagnetic insulating delta-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-O-2 phase above 96 GPa. We thus propose that zeta-O-2 should be base centered monoclinic with space group C2/m and four molecules per cell, suggesting a reindexing of the experimental diffraction peaks. Physical constraints on the intermediate-pressure epsilon-O-2 phase are also obtained.