  The main cause of the fragile-to-strong crossover of 3D silica was previously
attributed to the presence of a low energy cutoff in the potential energy
landscape. The important question emerges about the microscopic origin of this
crossover and the generalizibility to other glass-formers. In this work, the
fragile-to-strong crossover of a model 2D glassy system is analyzed via
molecular dynamics simulation, which represents 2D-silica. By separating the
sampled defect and defect-free inherent structures, we are able to identify
their respective density of state distributions with respect to energy. A low
energy cutoff is found in both distributions. It is shown that the
fragile-to-strong crossover can be quantitatively related to the parameters of
the energy landscape, involving in particular the low-energy cutoff of the
energy distribution. It is also shown that the low-energy cutoff of the
defect-states is determined by the formation energy of a specific defect
configuration, involving two silicon and no oxygen defect. The low-temperature
behavior of 2D silica is quantitatively compared with that of 3D silica,
showing surprisingly similar behavior.
