Creating grain boundaries in Lammps for ZnO wurtzite

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1

Hi Axel,

Thank you very much for all the insight and the indication of what to correct.

I did prefer to import a crystalline structure (read_data) instead of the lattice creation because I had some previous issues with this data you mentioned. It worked to read and join 2 ZnO crystals on the planes (0001) and (000-1) with a twist of 27.8° to create the grain boundary (GB). I’m also determining an outside region and group to delete and leave an orthorhombic assembly of 2 crystals.

Further I’ll need to use lx and ly of the box to calculate the GB area, but these remain with the value of the 2 triclinic boxes assembled. I’ve tried to use change_box to reestablish the box dimensions to the orthorhombic, but the follow error appears:

ERROR: Triclinic box skew is too large (…/domain.cpp:216)

Last command: change_box upper x final 5.18 26.18 boundary p p p set units box

Do you have any suggestions on how to change this box dimensions?

Thank you in advance!

Best,

Gustavo

Part of the script:

— Create Atoms

read_data ZnO_lower.xyz

region lower block INF INF INF INF INF INF

read_data ZnO_upper.xyz add append offset 0 0 0 0 0 shift 0.0 0.0 106.13642

region upper block INF INF INF INF INF INF

region outside block 5.18 26.18 22.72 49.89 0.00 212.28 side out

group upper region upper

group lower region lower

group outside region outside

change_box upper x final 5.18 26.18 boundary p p p set units box

#change_box lower x final 5.18 26.18 boundary p p p set units box

#change_box upper y final 22.72 49.89 boundary p p p set units box

#change_box lower y final 22.72 49.89 boundary p p p set units box

— Force Field

pair_style reax/c lmp_control

pair_coeff * * ReaxFF_Potential_ZnOpure O Zn

neighbor 2 bin

neigh_modify every 10 delay 0 check no

fix 1 all qeq/reax 1 0.0 10.0 1e-6 param.qeq

---------- Displace atoms and delete overlapping atoms ---------------------

#displace_atoms upper move 0 0 0 units box

delete_atoms overlap 1.0 lower upper

delete_atoms group outside

— Define Settings

compute csym all centro/atom 12

compute eng all pe/atom

compute eatoms all reduce sum c_eng

---------- Run Minimization ---------------------

…

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in.GB_S13_0001_tw_GBE.ZnO (3.25 KB)

2

if you prefer reading your base structures from files instead of using the lattice command, then i would suggest the following:

  • use the create_box command to create the box you want as the final with the number of atom types you need
  • do this with boundary f f f setting
  • make sure when importing coordinates, that you do so in the center of the box (otherwise atoms may be dropped due to the boundaries)
  • read_data allows to define a new group for the atoms imported, i would use that feature, especially when building even more complex structures, as you can then do the following steps in a convenient fashion
  • now first rotate the imported atoms in the way you want, then translate, then define the region you want to keep with side out, so that you can delete the atoms you want to remove easily.
  • repeat until you are done.
  • change the box boundary to p p p
  • check that you don’t have any close contacts due to PBC (they can be deleted with the delete_atoms command, if needed)

to explain the error. you need to keep in mind, that a) the various keywords of change_box are executed one after the other, b) when using read_data with add, the box may be expanded as needed and that may result in unwanted changes. c) changing the box positions in x won’t change its tilt, to turn that off, you need to set the tilt factors to 0.0. also, you probably don’t want the atoms being moved along the change of the box, which seems implied with your command line.

in summary and in my personal opinion, I think that figuring out how to use the lattice command as you need, is going to pay off in the long run and worth the hassle, but you can also get the same result with the approach you are following, only that it will always require more attention to detail and care how to run which commands in what order and to keep track of “side effects”.

axel.

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