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. [S0031-9007(98)07382-7].