A new high-pressure silica phase obtained by molecular dynamics

A molecular dynamics study with analytical and ab initio interatomic potentials revealed the possibility of a new silica phase with Pnc2 structure, which is more stable than stishovite and its CaCl2-like modification at pressures above approximately 120 GPa over a wide range of temperature. Our analysis of simulated X-ray diffraction patterns of various hypothetical post-stishovite phases shows that this new phase should be considered in the treatment of high-pressure experiments involving silica. The new phase might be responsible for the seismic discontinuity at 2728 km depth and should be treated as potentially stable at the pressures and temperatures of the lowermost mantle.