Fluctuations in Stress - Young's Modulus

Dear Users,

I am interested in determining the elastic modulus of polymers. I am following the below link to conduct simulations.

I am using a fix deform to apply a lateral strain in X-direction. However, stress (Pxx) shows large fluctuations.
After searching a few posts in the mailing lists, I have added fix ave/time based on Steve’s advice in one of the threads.
But that does not seem to help, still, there are large fluctuations in the stress. However, a lot of published papers show smooth stress vs strain profiles.

Could anyone help with this issue to obtain smooth stress vs strain profiles? I am pasting a few lines of input script.