High-pressure phase transition in sulfur

Elemental sulfur undergoes a complex sequence of structural phase transitions under high pressure, the understanding of which is crucial for revealing elemental behavior under extreme conditions. While experiments have identified multiple phases (e.g. S8 ring, S-II, S-III, S-IV, and [Formula: see text]-Po) up to 212[Formula: see text]GPa, structures at higher pressures ([Formula: see text] [Formula: see text]GPa) and within certain intervals (notably around 83–86[Formula: see text]GPa for the S-IV phase) remain uncertain. Here, we systematically predict the stable phases of sulfur from 100[Formula: see text]GPa to 600[Formula: see text]GPa using crystal structure searches performed with the CALYPSO method combined with first-principles density functional theory (DFT) calculations. Through enthalpy-pressure comparisons of candidate structures, we establish the phase transition sequence and corresponding transition pressures in this regime. Analysis of key interatomic distances further elucidates the structural reorganization accompanying each transition. Our results provide theoretical clarification for debated high-pressure phases (such as S-IV) and predict several previously unidentified stable phases along with their structural characteristics at pressures beyond current experimental reach. This work offers a coherent theoretical framework and predictive insights into the structural behavior of sulfur under extreme compression.