  We investigate the long time dynamics of a strong glass former, SiO2, below
the glass transition temperature by averaging single particle trajectories over
time windows which comprise roughly 100 particle oscillations. The structure on
this coarse-grained time scale is very well defined in terms of coordination
numbers, allowing us to identify ill-coordinated atoms, called defects in the
following. The most numerous defects are OO neighbors, whose lifetimes are
comparable to the equilibration time at low temperature. On the other hand SiO
and OSi defects are very rare and short lived. The lifetime of defects is found
to be strongly temperature dependent, consistent with activated processes.
Single-particle jumps give rise to local structural rearrangements. We show
that in SiO2 these structural rearrangements are coupled to the creation or
annihilation of defects, giving rise to very strong correlations of jumping
atoms and defects.
