Thermo output stress

Hi LAMMPS users,
I generated a polymer network model with several hundred polymer chains, each polymer chain include harmonic bond potentials, harmonic angle potentials and LJ excluded volume effects. In the equilibration stage, we used fix press/berendsen and fix langevin to control external pressure and temperature, respectively. Next, I used fix deform to stretch the simulation domain in x direction. The external pressure in y and z direction kept zero. The dumped figures also show that simulation domain indeed elongated in x direction.The thermo output stress pxx is not correct and it always fluctuates around zero. I confused why the output stress pxx is almost unchanged, whether I used some commands improperly? Any suggestions would be greatly appreciated. The input script is exhibited as follows, and the structure data file DN.data is attached.

Best wish!
Bo Gong

DN.data (39.7 KB)

What are you expecting to see? If you are expecting to see a modulus, but the modulus is in the low MPa to upper KPa range then it will likely be “drowned out” by the pressure fluctuations of the barostat. NEMD methods to determine mechanical properties for significantly soft materials are highly complicated because the signal-to -oise ratio is considered to be quite poor.

Best,
Dylan