Stress oscillation around zero

Hello users,

I have applied uniaxial strain in x-direction on tobermorite crystal using fix deform command. I have considered four cases, (1) CLAYFF potential, NVT ensemble with fix deform, (2) CSHFF potential, NVT ensemble with fix deform, (3) CLAYFF potential, NPT ensemble with fix deform, and (4) CSHFF potential, NPT ensemble with fix deform. Apart from these, I have tried time averaging with fix ave/time command for both CLAYFF and CSHFF potential. In all these cases, I am getting an stress oscillation around zero when I am considering compute stress/atom. But, in reality, it should increase and then decrease/fracture at a particular strain. What am I understanding wrong here? Any help will be greatly appreciated. Here’s a part of my code.


units real
atom_style full
boundary p p p

Bonded Interaction

bond_style morse
angle_style harmonic
dihedral_style harmonic
improper_style cvff

Non-Bonded Interaction

pair_style lj/cut/coul/long 10.0 10.0 # cutoff1 = 2.5*sigma
read_data data.14tclayff
kspace_style ewald 1e-6

#---------------------------MD simulation------------------------------------xxx
reset_timestep 0
compute peratom all stress/atom mobile_temp
compute p all reduce sum c_peratom[1] c_peratom[2] c_peratom[3] c_peratom[4] c_peratom[5] c_peratom[6]

Applying axial strain by fix deform

#fix 8 all nvt temp {temp} {temp} 5.0 drag 1
fix 8 all npt temp {temp} {temp} 5.0 y 0 0 1 z 0 0 1 drag 1
fix 9 all deform 1 x erate ${erate1} units box remap x
#fix 10 all ave/time 10 20 200 c_p[1] file temp.stress mode scalar