First-principles molecular dynamics simulations of the structure of germanium dioxide under pressures

We have carried out first-principles molecular dynamics simulations of glass and liquid germanium dioxide (GeO2) over a wide range of pressure. Our results show that in the glass GeO2 system nearly all Ge-O coordination environments are fourfold at low compression, whereas at high compression five- and sixfold coordination types coexist. In the liquid GeO2 system although most Ge-O coordination environments are fourfold, some threefold coordination types exist at low compression. Pentahedral units also exist in the liquid state while less than that in the glass state. At high compression, pentahedral units disappear and GeO6 octahedron is dominant in the liquid state going with some sevenfold coordination.