Structural, electronic and optical properties of a large random network model of amorphous SiO2 glass

The network bonding, electron states and optical excitation of a larger continuous random network (CRN) model of amorphous SiO2 (a-SiO2) glass with 432 SiO2 molecules (1296 atoms) are studied by first-principles methods. A previously constructed model with perfect Si and O coordination and periodic boundary condition is first relaxed by Vienna ab initio simulation package (VASP) with high accuracy. The final model with a density 2.202 gm/c.c. and very small bond length and bond angle distortions is obtained. The calculated electronic structure and optical properties of this CRN a-SiO2 glass are in very good agreement with experimental data. This model can serve as a base-line model for silica glass for further research on models containing defects, intentional doping or under high pressure. Comparison with crystalline α-quartz (α-SiO2) yields much insight on the subtle differences between a non-crystalline solid with no long range order and its crystalline counterpart with the same short range order.