European Physical Journal B
The structure of silica glass (SiO2) at different densities and at temperatures of 500 K is investigated by molecular dynamics simulation. Results reveal that at density of 3.317 g/cm3, the structure of silica glass mainly comprises two phases: SiO4- and SiO5-phases. With the increase of density, the structure tends to transform from SiO4-phase into SiO6-phase. At density of 3.582 g/cm3, the structure comprises three phases: SiO4- , SiO5-, and SiO6-phases, however, the SiO5- phase is dominant. At higher density (3.994 g/cm3), the structure mainly consists of two main phases: SiO5- and SiO6-phases. In the SiO4-phase, the SiO4 units mainly link to each other via corner-sharing bonds. In the SiO5-phase, the SiO5 units link to each other via both corner- and edge-sharing bonds. For SiO6-phase, the SiO6 units can link to each other via corner-, edge-, and face-sharing bonds. The SiO4-, SiO5-, and SiO6-phases form SiO4- SiO5- and SiO6-grains respectively and they are not distributed uniformly in model. This results in the polymorphism in the silica glass at high density.