GPa. However, the agreement with experimental results is only partial: for example, in the case of dioxolane silica SOD, a transition from cubic to rhombohedral was observed at pressures higher than 1.2 GPa, with the trigonal space group being either R3m or R3. This discrepancy with the ab initio calculations is likely due to the constraints adopted in the simulations, which preserved the cubic symmetry of the lattice. All the studies indicated the increase in the tilting of the silica tetrahedra as main mechanism of compression underlying the phase-transition Im3̅ m/ I4̅ 3m, which is supposed to be continuous. On all-silica SOD, the pressure-induced amorphization has not been reported in any experimental work.