  We compare the ability of various interaction potentials to predict the
structural and mechanical properties of silica and sodium silicate glasses.
While most structural quantities show a relatively mild dependence on the
potential used, the mechanical properties such as the failure stress and strain
as well as the elastic moduli depend very strongly on the potential, once
finite size effects have been taken into account. We find that to avoid such
finite size effects, samples of at least 75,000 atoms are needed. Finally we
probe how the simulation ensemble influences the fracture properties of the
glasses and conclude that fracture simulations should be carried out in the
constant pressure ensemble.
