Phase Stability of Solid Oxygen at high pressure

The high-pressure phase stability of solid oxygen remains a subject of active investigation, despite significant theoretical and experimental efforts. While the ε₀–ε transition above 20 GPa is now established, the atomic structure associated with this transition remains poorly understood. In this study, we re-examine the stability of solid oxygen using density functional theory with a hybrid exchange-correlation functional. By integrating static structure searches with ab initio molecular dynamics simulations at 300 K, we identify the Pm phase as the most stable structure above 111 GPa. Our predictions are further evaluated against existing experimental observations from X-ray diffraction, spectroscopic, and superconductivity measurements, providing insights into the competing high-pressure phases of oxygen.