Crystal Structure and Superconductivity of PH3 at High Pressures

We have performed a systematic structure search on solid PH3 at high pressures using the particle swarm optimization method. At 100-200 GPa, the search led to two structures which along with others have P-P bonds. These structures are structurally and chemically distinct from those predicted for the high-pressure superconducting H2S phase, which has a different topology (i.e., does not contain S-S bonds). Phonon and electron-phonon coupling calculations indicate that both structures are dynamically stable and superconducting. The pressure dependence and critical temperature for the monoclinic (C2/m) phase of 83 K at 200 GPa are in excellent agreement with a recent experimental report.