I am trying to find out stress strain plot for a amorphous polymer cell at 300K. Am using “fix deform” to applying strain rate of 1e-4 along x direction. The size of my simulation cell is 250 x 250 x 250 angstroms.
The strain rate am using is very high compared to the experimental strain rate. Here the bonded energy contribution is high compared to nonbonded energy, but it should be the other way.
So, I tried to simulate with a strain rate of 1e-7, the stress strain plot is so fluctuating I couldnt get the modulus values, or even the pattern of the plot is not found.
I have crossed checked the parameters and am using charmm forcefield which was used for polymers from literature.
Can anyone get me some idea why there is large fluctuation in the stress strain plot.
Following is the command I am using
fix 1 all npt temp 300 300 5 y 0 0 50 z 0 0 50 drag 1
fix 2 all deform 1 x erate 1e-7 units box remap x