Fig. S2.
The packing fraction of the atoms against pressure. Comparing the total packing (Si + O) against the oxygen packing shows that at low pressures, the total packing is mainly induced by the oxygen atoms, whereas at higher pressures, the Si atoms become more and more important. The total packing fraction seems to be more or less constant within error bars >25 GPa and never rises above the total packing fraction of the predicted crystalline Fe2P-type structure of SiO2 at ultrahigh pressures (640 GPa) (30). The data are compared with the optimal closed packing of equal spheres defined by the KC at 0.74 and to the optimal RCP of equal spheres at 0.64.