I am trying to perform uniaxial deformation of HDPE polymer in lammps using ReaxFF forcefield. Prior to deformation, I run energy minimization to force tolerance 1 Kcal/(mol A) and then NPT to get my polymer density to 1 g/cm3 as in the literature and run NVT to relax in constant volume ensemble.Thenafter performed deformation. During deformation, the stress in x-direction is scattering between 1.5 to -1.5 (GPa) and I am unable to find the modulus of the polymer. Is there any error in my input file?
Thanks for your help!
My Input script and deformation log file are below:
variable simname index PE_nc10_cl1000
Stresses do fluctuate so that is normal. Please discuss with your advisor on how to deduce modulus from stress-strain curves.
Thanks for your valuable suggestions.
As a follow-up above is an image of the stress strain data. I am really not seeing any portion here that resembles a curve and it is making me think I have some error in my input script. As mentioned above,prior to deformaiont I:
- Run energy minimization to force tolerance 1 Kcal/(mol A)
- NPT to get my polymer density to 1 g/cm3 as in the literature
- NVT to relax in constant volume ensemble.
The stress is then taken from the pressure in the x direction (the direction of deformation).
Any help would be much appreciated as I am still new to building polymers.