CNT strength confirmation with various BCs

Dear Lammps users;

im modeling a cnt under compression and i want to extract the fracture strength of the model under CC and SS boundary conditions. The result should be 4x times higher for CC with respect to SS one. unfortunately i cannot get the proper result. im getting good result for SS bc and i can verify it with other papers that exist, but i get lower result for CC and i dont know what is wrong.

im using serforce 0 0 0 for CC bc with 4 layers of atom at the ends. the fix nve is set for whole model and fix nvt is set for mid part. and im using fix move for moving the sides to the mid sections. will you please tell which part it is that im doing wrong or show me sample code?

i have posted a sample code beneath

thanks in advance

Hamed Badjian

dimension 3
boundary s s s
units metal

read_data ./88data.txt
log ./Stress-Strain.txt

pair_style airebo 1 0 0
pair_coeff * * CH13.airebo C

region 1 cylinder z 0 0 20 105 INF
group right region 1

region 2 cylinder z 0 0 20 INF 4
group left region 2

group side union left right
group mid subtract all side

velocity all create 300 2983742 mom yes dist gaussian

fix f3 all nve
fix f4 mid temp/rescale 100 300 300 0.5 0.8
fix f1 side store/force
fix f2 side setforce 0 0 0

timestep 0.001
minimize 0 0 10000 1000

fix f5 right move linear 0.0 0.0 -0.02 units box
fix f6 left move linear 0.0 0.0 0.02 units box

compute cmaxxx right property/atom fx fy fz
#fix 9 all ave/atom 1 1 1 c_cmaxxx[1] c_cmaxxx[2] c_cmaxxx[3]
compute cmaxx right reduce max c_cmaxxx[1]
compute cmaxy right reduce max c_cmaxxx[2]
compute cmaxz right reduce max c_cmaxxx[3]
compute cmaxxf right reduce max f_f1[1]
compute cmaxyf right reduce max f_f1[2]
compute cmaxzf right reduce max f_f1[3]
compute cmaxzf2 all reduce max f_f1[3]

variable l0 equal 110
variable EngVol equal (12468.21)(10^4)
compute stN11 all stress/atom NULL
compute stN13 all reduce sum c_stN11[3]
variable Sgiga1 equal (c_stN13)/(${EngVol})
variable Sgiga1Positive1 equal (v_Sgiga1)

dump d1 all xyz 10

variable strain equal ((step-500)(0.04)(0.001))/(${l0})

thermo 10
thermo_style custom step temp ke pe press lz v_strain v_Sgiga1Positive1 c_cmaxz c_cmaxzf c_cmaxzf2
fix stressstrain all print 100 “{strain} {Sgiga1Positive1}” file ss.txt screen no
run 1000000