Low Energy Dynamics and Tunneling States in Silica Glass

We present the results of a simulation study of silica glass which addresses the issue of large-amplitude low energy motions involving reorientations of SiO₄ tetrahedra. Using methods developed for crystalline silicates we find that random networks of linked SiO₄ tetrahedra are as flexible as crystalline phases for infinitesimal displacements. Patches of the networks can also undergo large sudden distortions involving reorientations of the SiO₄ tetrahedra, with little change in energy and an energy barrier of around 0.06 eV. These may act as tunneling states to provide the mechanisms for the anomalous low-temperature thermal properties of glasses.