Fig. 5. Chemical potential of S vapours per mole of atoms, given at several pressures according to range of calculation methods. Data for S2 and S8 are also provided from the thermochemical literature.3 At low pressures, the free energy diverges by more than 50 kJ mol–1 S atoms between the S2 and S8 allotropes at high temperatures, while at high pressures there is less variation. Results from hybrid DFT calculations with scaled frequencies closely track the minimal value from the literature, while the local and semi-local exchange–correlation functionals diverge from this data due to over-estimation of the formation energy of S2.
