The lowest energy structure found for the structure. We considered 10 possible distributions for the partially occupied B13 and B16 sites with the energies in Table 1 (the structures are in Ref. [8]). The lowest is S2 while the energies of S8 and S7 are only 0.2 and higher. The lowest energy structure has the same B13 and B16 sites as although this structure breaks the symmetry along the twin boundary. These B13 sites are shown as purple while the B16 sites are red with all other sites green. The definition of various sites in can be found in Ref. [10].
Helmholtz Free energy differences of and relative to as a function of temperature [9]. The red dashed curve uses the phonon calculations for the 106 atom crystal unit cell and the 212 atom crystal unit cell . This indicates that may be more stable than at temperatures above 950 K. We consider that comparing the phonon contributions for systems with two different numbers of atoms per cell might bias the corrections because of the particular sampling of the Brillouin zone, so we recalculated the phonon corrections for using the doubled unit cell (212 atoms). This leads to the solid black line, indicating that the phase is the most stable phase until the melting temperature of 2350 K.