In order to obtain stress-strain curve from MD simulation, two approaches are possible, one is applying external strain and the other is applying external stress.
The former is supported by the command fix deform.
And the latter can be achieved via the fix npt aniso.
In the latter case, how often the pressure is updated to a new value?
For example below, the overall stress rate becomes 1000atm/100ps = 10atm/ps in units real.