Revisiting the electronic and optical properties of SiO2 polymorphs by hybrid functional calculations

Abstract

The structural, electronic, and optical properties of nine different polymorphs of silica are investigated with both the traditional generalized gradient approximation (GGA) scheme and the hybrid functional. These include the 4:2-coordinated systems of quartz, tridymite, cristobalite, coesite, and keatite, as well as the 6:3-coordinated stishovite. The phases with similar crystal structures tend to share analogous electronic and optical features, while these properties are different in the case of stishovite. For the 4:2-coordinated polymorphs, linear relations are firmly established between the bandgap and the static dielectric constant vs the unit cell volume, respectively. Further investigation of their refractive indices also reveals a strong linearity with the corresponding densities. Our calculation with the sX functional reproduces the experimental bandgap values well, while GGA is superior for the overall trends of their optical properties.