Fig. 2. Ground-state energies from DFT of clusters included in study. Energies are relative to the energy for S₈ with each functional, and normalised to the number of atoms. A point is also included from reference data;3 this is derived from the enthalpies of formation at zero temperature, based on spectroscopic observations and equilibrium studies. While the energies from different exchange–correlation functionals diverge across the series, the S₂ energy from PBE0 calculations agrees closely with this reference data.