  Relaxation phenomena in glasses can be related to jump processes between
different minima of the potential energy in the configuration space. These
transitions play a key role in the low temperature regime, giving rise to
tunneling systems responsible for the anomalous specific heat and thermal
conductivity in disordered solids with respect to crystals. By using a recently
developed numerical algorithm, we study the potential energy landscape of
silica clusters, taking as a starting point the location of first order saddle
points. This allows us to find a great number of adjacent minima. We analyze
the degree of cooperativity of these transitions and the connection of physical
properties with the topology of the configuration space. We also identify
two-level systems (pairs of minima constituting a tunneling system) and
calculate the quantum mechanical ground state splitting by means of the WKB
approximation.
