Stress-strain oscillation tobermorite simulation

Hello everyone,

I am trying to obtain the stress-strain curve of tobermorite 14A with LAMMPS using CLAYFF potential. For non-bonded energy, lj/cut/coul/long was used. I am running into several issues here. I am using fix deform to deform the simulation box. For equilibration I am using fix nve and fix npt. After the equilibration, I am deforming the box in x-direction. Two things happened here: 1) If I commented out the fix/nvt part, the stress kept on increasing, 2) If I keep the fix/nvt part, the stress oscillates around 0. But ideally, the stress should increase and then fracture after a particular strain.

Because tobermorite consists water, should I use fix/shake? If I used fix/shake, before the equilibration, I am running into “non-numeric positions” errors. Can anyone help me with the solution? Here’s a part of my input file.

Bonded Interaction

bond_style morse
angle_style harmonic
dihedral_style harmonic
improper_style cvff

minimize 1.0e-4 1.0e-6 100 1000
min_style cg
min_modify dmax 0.1

fix 5 water shake 0.0001 20 10 b 5 a 8 t 6 7 m 15.999400 1.007970
fix 1 all nve
fix 2 all langevin {temp} {temp} 5.0 2341456

fix 10 all langevin {temp} {temp} 5.0 2341456
fix 9 all deform 1 x erate ${erate1} units box remap x

timestep 1
thermo 100
thermo_style custom temp v_strainx v_sigmax
run 30000