Study Of Compressed Sulfur Based On Reliable First-Principles Calculations

We investigated the high-pressure phases of sulfur using first-principles calculations with high precision. In a previous study, Rudin et al. [Phys. Rev. Lett. 83. 3049 (1999)] predicted that the beta-Po type rhombohedral structure is followed by a simple cubic (sc) structure. Strictly limiting the comparison to the work of Rudin et al. and four atoms per unit cell, our high-precision calculations that couple an originally developed structure search method demonstrate that the proposed sc structure is not the ground state at any pressure value, and that compressed S undergoes a first-order phase transition to a body-centered-cubic phase above 500 GPa. The potential energy surface constructed by the pseudopotential employed by Rudin et al. does not conform with that constructed by an all-electron calculation. Our findings extensively contribute to the ongoing effort in forming an accurate picture of the structural phase transitions of compressed S, and also brings to light the importance of careful treatments necessary when calculating high-pressure states using the pseudopotential method.