I am a new user of LAMMPS software. Recently, when conducting uniaxial tensile simulation of SiC, I was puzzled by the following questions:
When I used velocity command to simulate stretching, I found that the workpiece began to vibrate continuously after being pulled off, and the SiC at a given initial speed no longer moves.
The in file is as follows：
initialization
echo screen
dimension 3
boundary s s s
units metal
atom_style atomic
#modeling
lattice custom 4.36 a1 1.0 0 0 a2 0 1.0 0 a3 0 0 1.0 &
basis 0.0 0.0 0.0 &
basis 0.5 0.5 0.0 &
basis 0.5 0.0 0.5 &
basis 0.0 0.5 0.5 &
basis 0.25 0.25 0.25 &
basis 0.75 0.75 0.25 &
basis 0.75 0.25 0.75 &
basis 0.25 0.75 0.75 &
orient x 1 1 1 &
orient y -1 -1 2 &
orient z 1 -1 0
region reaction cylinder x 0.0 0.0 25.0 5.0 145.0 units box
region rigid1 cylinder x 0.0 0.0 25.0 0 5.0 units box
region rigid2 cylinder x 0.0 0.0 25.0 145 150 units box
region nano_sic union 3 reaction rigid1 rigid2
create_box 2 nano_sic
create_atoms 2 region nano_sic &
basis 1 2 &
basis 2 2 &
basis 3 2 &
basis 4 2 &
basis 5 1 &
basis 6 1 &
basis 7 1 &
basis 8 1
mass 1 12.01
mass 2 28.09
group rigid11 region rigid1
group rigid22 region rigid2
group workpiece region reaction
velocity rigid11 set 0.0 0.0 0.0
velocity rigid22 set 0.0 0.0 0.0
velocity workpiece create 300 13221 dist gaussian
pair_style tersoff
pair_coeff * * SiC.tersoff C Si
neighbor 0.3 bin
neigh_modify delay 10 every 1 check yes
The relaxation process
minimize 1.0e-4 1.0e-6 10000 100000
fix 10 rigid11 setforce 0.0 0.0 0.0
fix 20 rigid22 setforce 0.0 0.0 0.0
fix 30 all nvt temp 300 300 1.0
reset_timestep 0
timestep 0.001
thermo 100
thermo_style custom step pe ke temp
run 50000
calculate strain and stress
reset_timestep 0
variable L_x equal “lx”
variable L0 equal ${L_x}
variable strain equal “(lx-v_L0)/v_L0”
compute v workpiece voronoi/atom
compute s workpiece stress/atom NULL
compute 2 workpiece reduce sum c_s[1] c_s[2] c_s[3] c_v[1]
variable stressx equal c_2[1]/c_2[4](1.0e-4)
variable stressy equal c_2[2]/c_2[4](1.0e-4)
variable stressz equal c_2[3]/c_2[4](1.0e-4)
thermo_style custom step temp v_stressx v_stressy v_stressz
fix def3 workpiece print 100 “{strain} {stressx}” file stress-strain.txt screen no
dump 1 all custom 500 ./dump/strentch..lammpstrj id type x y z vx vy vz
velocity rigid22 set 0.09 0.0 0.0
run 80000
write_data stretch_repetition.data