SIA diffusion in BCC iron

LAMMPS LAMMPS Mailing List Mirror
1 
Hi LAMMPs community,

I've been involved in calculating the iron migration energy in BCC Fe 

for a while, but unfortunately I am not getting to the amount mentioned in

 the references (0.34 eV). I considered three atoms (1, 2 and 3 in figure) had to migration 

(due to initial and final dumbbell form), but when i forced the atom 2 migrate to the center


and atoms 1 to the corner i gave ~EBR=1e-10 and when atom 2 migrate to the corner

and atom 1 to the center i gave ~5.5. I really dont know what is wrong, I appreciate

any suggestion. The other thing is how can i give energy barrier plot (like figure)?

image.png

2

You don’t say how you are computing the energy changes or “forcing”
things to happen. This seems like a calculation for NEB, see the neb command
in LAMMPS. It can produce data for barrier plots like you show.

Steve

image.png

3

Hi Steve
Thanks for answering

Yes, I am using NEB and i used the following commands for neb and non-neb atoms:
fix 2 nonneb setforce 0.0 0.0 0.0
fix 3 nebatoms neb 10.0

i don’t think that this is the problem and i do i saw the NEB command in LAMMPS.
(i know this is not a LAMMPS problem): I do not know what is the criteria in SIA migration.

i mean i do not know (according to the figure) that i should start with 10 atoms (one of them is an extra migrating atom) or with
9 atom (one of them is a migrating atom that is displaced from its position). However, my latter case gave me some better results!
maybe the crucial question is: Do we need to add an extra atom or not, in order to simulate migration energy using NEB?

image.png