  Via computer simulations of the standard binary Lennard-Jones glass former we
have obtained in a systematic way a large set of close-by pairs of minima on
the potential energy landscape, i.e. double-well potentials (DWP). We analyze
this set of DWP in two directions. At low temperatures the symmetric DWP give
rise to tunneling systems. We compare the resulting low-temperature anomalies
with those, predicted by the standard tunneling model. Deviations can be traced
back to the energy dependence of the relevant quantities like the number of
tunneling systems. Furthermore we analyze the local structure around a DWP as
well as the translational pattern during the transition between both minima.
Local density anomalies are crucial for the formation of a tunneling system.
Two very different kinds of tunneling systems are observed, depending on the
type of atom (small or large) which forms the center of the tunneling system.
In the first case the tunneling system can be interpreted as a single-particle
motion, in the second case it is more collective.
