Uniaxial Tension Simulation Stops Before Fracture

Hello All,

I am trying to load a crystal to fracture under uniaxial tension in LAMMPS version dated 23 Jun 2022. The simulation proceeds without errors until the stress-strain curve flattens and starts to assume a negative slope, at which point it exits due to one of the two following errors:

  1. ERROR: Lost atoms: original 53125 current 53123
  2. ERROR on proc 217: Out of range atoms - cannot compute PPPMDisp

Due to these errors, I cannot take the system all the way to fracture. Furthermore, at these final stages of the simulation (i.e., once the stress-strain curves flattens and starts to assume a negative slope), in addition to these errors, I sometimes observe that the temperature suddenly drops all the way to zero despite being in the NPT ensemble at 300 K.

Any suggestions for extending the simulation all the way to fracture is appreciated.

INPUT (units metal used here):


read_restart restart.file

Potential Parameters

pair_style buck/long/coul/long long long 12
kspace_style pppm/disp 1e-5
kspace_modify force/disp/real 4.335e-6
kspace_modify force/disp/kspace 8.671e-5
“list of pair coefficients here”

Simulation Specifics

variable atm equal 0
timestep 1e-3 # in PICOSECONDS
neigh_modify every 5 delay 0 check yes
restart 20000 restart.file
fix 1 all npt temp 300 300 0.1 x {atm} {atm} 1 y {atm} {atm} 1
fix 2 all deform 1 z erate 0.0004 units box remap x
variable stp equal “step”
variable len_z equal “lz”
variable tmpr equal “temp”
variable plat_x equal “pxx/10000”
variable plat_y equal “pyy/10000”
variable pz equal “pzz/10000”
fix dp all print 200 “{stp} {len_z} {plat_x} {plat_y} {pz} {tmpr}” file opdat screen no
thermo 200
thermo_style custom step lz press temp
compute p all stress/atom NULL
dump data all custom 200 dump.data id type mass x y z vx vy vz c_p[*]
run 480000

Is the potential you are using suitable for your study? I have some serious doubts there.
Most Buckingham potentials may only be used for regular bulk systems and are not suitable for anything where you stray too far from the crystal geometry.