Crucial role of S-rings in structural, relaxation, vibrational, and electronic properties of liquid sulfur close to the λ transition.

Liquid sulfur has been studied by density-functional based molecular dynamics simulations at different temperatures ranging from 400 up to 700 K across the well-documented λ transition. Structure models containing either a majority of S chains or S rings are considered and compared to experimental data from x-ray scattering. The comparison suggests a liquid structure of a majority of twofold sulfur at low temperature, dominated by S rings that open progressively upon temperature increase. Typical features associated with such rings are analyzed and indicate that they contribute to a specific third correlating distance in the pair correlation function and to a contribution at low wavevector k in the reciprocal space. The vibrational properties of liquid sulfur are also considered and indicate a contribution at 60 meV that is associated with both chains and rings, albeit the latter lead to a more intense peak at this wavenumber. The underlying network structure also impacts the dynamic properties of the melts which display enhanced dynamic heterogeneities when S rings are present. The analysis of the electronic Kohn-Sham energies shows insulating character with a gap of about ≃2.0 eV, albeit the presence of localized mid-gap states is acknowledged that can be associated, in part, with the presence of S rings.