Dear Lammps users,
I am using fix deform command to obtain Young’s modulus and shear modulus. When I run the the following script, I encountered two problems:
I can get reasonable Young’s modulus when the stretching strain is small (<5%). The tensile stress (uniaxial) of graphene is expected to abruptly drop down when the strain reaches around 20%. But my obtained stress keeps increasing. It seems that the graphene can not be broken down even the strain is already large enough (>30%).
When I use “fix deform” to tilt the box, the shear stress in xy direction (pxy if I understand correctly) fluctuates and does not increase with the shear strain.
I searched related topics in the threads, but did not find any solution. Could anyone pointed out the problems/errors in my script and give me some advices?
boundary p p p
pair_style airebo 2 1 0
pair_coeff * * CH.airebo C
fix 1 all npt temp 300 300 0.5 y 0 0 0.5
compute 1 all stress/atom NULL
compute 2 all pe/atom
compute 3 all reduce sum c_1 c_1 c_1
thermo_style custom step temp pe ke etotal lx ly xy pxx pyy pxy
fix 1 all nvt temp 300 300 50
fix 2 all ave/atom 1 1000 1000 c_1 c_1 c_1 c_2 fx fy fz
dump 1 all atom 1000 dump.lammpstrj
fix 3 all deform 1 y erate 0.001 units box remap x (tensile strain, for Young’s Modulus)
fix 3 all deform 1 xy erate 0.001 units box remap x (shear strain, for Shear Modulus)
Thanks in advance for your time and assistance.