Dear Lammps Users,
I’m trying to obtain stress-strain curve of a 2D material such as graphene but anisotropic one which means it’s young modulus deffer in x axis and y axis, to do so I used fix deform to perform an engineering strain in one direction on my system and computing stress as below.
echo screen
boundary p p s
atom_style atomic
units metal
read_data datafile
mass * 30.974
pair_style eam/alloy
pair_coeff * * FeP.lammps.eam P
dump mydump1 all atom 3000 dump.lammpstrj
velocity all create 300 94621546 rot yes mom yes
thermo 1000
thermo_style custom step temp lx ly lz vol
timestep 0.001
compute stress all stress/atom virial
compute Rstress all reduce sum c_stress[2]
variable ystrs equal -c_Rstress/lx/ly/5.58/10000
variable ystrain equal (ly-97.709)/97.709*100
fix avg1 all ave/time 3 1000 3000 v_ystrs v_ystrain file ystrs.txt
fix NPT all npt temp 300 300 0.1 x 0 0 1 y 0 0 1
run 9000
unfix NPT
fix 1 all deform 1 y erate 0.0002 remap v
fix NVT all nvt/sllod temp 300 300 0.1
run 10000000
In fact I want the other direction stress-free but I found out when I use fix deform in x direction the other side remain fix and if I use it I have negative stress on the other direction too. but I want it to be stress-free like when we use NPT.
Is there any approach to solve this problem? or any other method to use for this problem?
Thanks