Phase transition and superconductivity of selenium under pressure

Although a substantial amount of research has been conducted to unravel the structural configurations of selenium under pressure, the exquisite sensitivity of selenium's p-orbital electrons to this external force, leading to a plethora of structural variations, leaves several intermediary phases still shrouded in mystery. We, herein, systematically identify the structural and electronic transformations of selenium under high pressure up to 300 GPa, employing crystal structure prediction in conjunction with first-principles calculations. Our results for the transition sequence (P3₁21 → C2/m → R3̄m → Im3̄m) of selenium are in good agreement with experimental ones. In particular, we first clarified the knowledge pertaining to the atomic arrangement within the monoclinic C2/m phase of selenium. Electron-phonon coupling calculations indicate that the superconductivity observed in this material, akin to that in tellurium, is realized via a phase transition. Furthermore, the superconducting critical temperature (T_c) displays a consistent rise as the material experiences high-pressure phase transitions from C2/m to R3̄m and then to Im3̄m, achieving a maximum T_c of 13.06 K in the Im3̄m phase at 97.5 GPa. Our findings illuminate the path towards a deeper comprehension of the high-pressure structure and physics of selenium, prompting the need for innovative experimental and theoretical research.