stress distribution after equilibration

Dear lammps-users and developers,

I want to do a simulation about indenting and then to analyze the stress distribution in the indented substrate with the command “compute stress/atom” and “compute voronoi/atom”.

At first, I equilibrated the substrate(without the indenter) 80ps with a npt ensemble, but the stress field looks oddly after the equilibration because the absolute value of the final six stress vectors is much larger than that of the initial state. Is this phenomenon reasonable or is there any problems in my input script?

The input script shown follow (tha 11 Sep 2015 version LAMMPS was used on a linux platfom):

log log.equal
units metal
boundary p p p
timestep 0.001

Zincblende SiC

lattice diamond 4.3211699
region box block 0 8.0 0 8.0 0 8.0
create_box 2 box
create_atoms 1 box basis 5 2 basis 6 2 basis 7 2 basis 8 2
mass 1 28.086000
mass 2 12.011150

Choose potential

pair_style tersoff
pair_coeff * * SiC.tersoff Si C

Setup neighbor style

neighbor 1.0 nsq
neigh_modify once no every 1 delay 0 check yes

compute str all stress/atom NULL
compute vor all voronoi/atom only_group

variable pxx atom c_str[1]/c_vor[1]/10000 # units GPa
variable pyy atom c_str[2]/c_vor[1]/10000
variable pzz atom c_str[3]/c_vor[1]/10000
variable pxy atom c_str[4]/c_vor[1]/10000
variable pxz atom c_str[5]/c_vor[1]/10000
variable pyz atom c_str[6]/c_vor[1]/10000

velocity all create 293.15 825577 dist gaussian
fix NPT all npt temp 293.15 293.15 0.1 iso 0.0 0.0 1

Setup output

thermo 1000
thermo_style custom step temp etotal press lx ly lz vol
thermo_modify norm no

dump 1 all custom 1000 dump.equal1 id type x y z c_str[1] c_str[2] c_str[3] c_str[4] c_str[5] c_str[6] c_vor[1] c_vor[2]
dump 2 all custom 1000 dump.equal2 id type x y z v_pxx v_pyy v_pzz v_pxy v_pxz v_pyz

run 80000

Any suggestion would be appreciated.


this is a question, that you should be able to answer yourself (it is
worth thinking about this for a bit).
here are a couple of hints:
- what kind of structure do you generate initially?
- and what is it that you are doing during equilibration? why do you
need to do an equilibration?


p.s.: please don't use brightly colored rich formatted text. it is
*extremely* unpleasant to read.