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


From: Jan Fikar <fikar@...6994...>
Date: Mon, 4 Sep 2017 12:58:27 +0200

If you want the formation energies of unstable SIAs, just do the
minimize. Completely skip the dynamics at 30K as this may lead to
unpredictable results. You better check what is the real configuration
of atoms after minimize.

BTW. why would you first remove one atom? Usually formation energy of
SIA is the energy of the block of n+1 atoms - (n+1) times energy of
perfect atom, which is energy of perfect block of n divided by n.

Jan

On 09/04/2017 12:36 PM, Bom Salman wrote:
> 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
> 
> 
> 
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