  We perform molecular dynamics simulations for a silica glass former model
proposed by Coslovich and Pastore (CP) over a wide range of densities. The
density variation can be mapped onto the change of the potential depth between
Si and O interactions of the CP model. By reducing the potential depth (or
increasing the density), the anisotropic tetrahedral network structure observed
in the original CP model transforms into the isotropic structure with the
purely repulsive soft-sphere potential. Correspondingly, the temperature
dependence of the relaxation time exhibits the crossover from the Arrhenius to
the super-Arrhenius behavior. Being able to control the fragility over a wide
range by tuning the potential of a single model system helps us to bridge the
gap between the network and isotropic glass formers and to obtain the insight
into the underlying mechanism of the fragility. We study the relationship
between the fragility and dynamical properties such as the magnitude of the
Stokes-Einstein violation and the stretch exponent in the density correlation
function. We also demonstrate that the peak of the specific heat systematically
shifts as the density increases, hinting that the fragility is correlated with
the hidden thermodynamic anomalies of the system.
