Classical molecular dynamics simulations of behavior of GeO₂ under high pressures and at high temperatures

Abstract

We have investigated the high-pressure and high-temperature behavior of GeO₂ with the help of extensive molecular dynamics simulations. Our calculations show that α-GeO₂ transforms reversibly to a denser and higher-coordinated (Ge-O) monoclinic phase at ~8 GPa, reasonably close to the experimental observation of 7.8 GPa. Our simulations on vitreous GeO₂ show that, at higher pressures, substantial numbers of Ge atoms are coordinated with five oxygen atoms. However, our results do not support the existence of an entirely pentahedrally coordinated state, claimed to have been observed recently. The simulations on the liquid phase, carried out at several temperatures, display the existence of a first-order phase transition under compression. Our results suggest that this may not be a low-density to high-density liquid-liquid transformation as the denser phase is found to be solidlike. These results suggest the necessity of a more careful characterization of the high pressure phase obtained from compression of the liquid phase in the experiments.