Microstructure and polyamorphism of amorphous SiO2 at 500 K and 0÷20 GPa were investigated by molecular dynamics simulation. The results indicate that in the studied pressure range, the network structure of amorphous SiO2 includes SiOx structure units (x = 4, 5, 6) and OSiy (y = 2, 3). The two-state model (high density and low density) is used to describe the network structure of the amorphous SiO2. High-density phase is formed by SiO5 and SiO6 linked via OSi3, low-density phase is formed by SiO4 linked via OSi2. The proportion of high density phase and low density phase depend on pressure.
