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[lammps-users] About SIA (or defect) insertion, how to fix the symmetry
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[lammps-users] About SIA (or defect) insertion, how to fix the symmetry


From: Bom Salman <bombomsalman@...24...>
Date: Mon, 4 Sep 2017 19:36:25 +0900

Dear All

My question about, that I have tried to insert an SIA interstitial into crystal structure like iron,
has maybe 2000 atoms,
what I did:
remove one atom form perfect structure and place two atoms instead which will simulate the SIA dummbel, but my problem is when I try to find how it is different in term of formation energy between <111> SIA dummbel and <110> SIA dummbel, I see the results out of expectation. since it is known that the formation energy for <110> is lower than the formation energy of <111> SIA defects but my result is opposite.

this because the once we do the simulation these interstitials reorganize into a more stable configuration. Therefore the energy that I have assigned to a particular orientation (my initial one) may correspond to a different configuration (the relaxed).
 

this the script I used to find the formation energy:

############################################

units  metal
boundary  p p p
atom_style atomic
atom_modify map array
read_data   data.after_SIA_added
pair_style eam/fs
pair_coeff * * Fe_ackland.eam.fs  Fe

group vanadium  type 1

velocity  all create 30.0 1 mom  yes rot yes  dist gaussian

timestep 0.001 #corresponding to 1 fs

thermo_style custom step temp pe ke etotal press vol xlo xhi ylo yhi zlo zhi
thermo 100


fix 1 all nvt temp 30.0 30.0 0.1  #  all related pressure values deleted ,no need for iso 0.0 0.0 1.0   
restart 50000 restart.fe-30K
run 100000
minimize 1.0e-16 1.0e-16  2000 6000
######################################

then is there a way to fix the symmetry? like how can we get energies for dumbbells. even if it is not stable and is that would be reasonable to approach?


Thank you