Extended Data Fig. 2: Ionic bonding of v-SiO₂.

Mulliken atomic charges for Si (a) and O (b), and the average Mulliken ionicity of the Si-O bond (c) in v-SiO₂ as a function of pressure. The results (circles) are compared with those corresponding to different SiO₂ crystalline polymorphs. The error bars in (b) correspond to the standard deviation of the average of the charges of all O atoms. Similar relative errors were estimated for (a) and (c).