Finally, once 300 K is reached, we switched to the constant-pressure (N, P, T ) ensemble at P = 0 Pa, with a pressure damping parameter of 1000 fs and using an isotropic cell. After a short equilibration period of 30 ps, we found that this constant-pressure simulation led to an increase in density from 1.21 to 1.3. We checked that using a longer equilibration period of 500 ps does not change the properties of the resulting glass. We tried using a flexible cell (LAMMPS keyword tri) and found that it led to a dramatic increase in density (up to 1.6),