Static structure and dynamical correlations in high pressure H₂S

The structure and dynamics of H₂S phase IV is investigated via first-principles calculations. The weakness of the hydrogen bonding allows for slow rotational flipping and large fluctuations of the S atoms around their average positions. The S motion is large and correlated and is responsible for the presence of short S-S bonds that are created and destroyed in a dynamical fashion. Our simulated structure, compatible with experimental scattering data, differs from the previous static models: dynamical correlations in the S positions are essential for a correct description of H₂S phase IV.