error in forming <111> crystal direction

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1

Hii,

If I orient <111> direction of a BCC crystal to the z direction of the simulation box using the command given below. The simulation box formed showed dislocation (using DXA in OVITO) even at time t=0 on all the surface.(which is not how my initial crystal should be)

lattice bcc ${alat} origin 0.0 0.0 0.0 orient x 1 -1 0 orient y 1 1 -2 orient z 1 1 1

These initial dislocations is not seen if I make the crystal outside using external package and read the positions of atoms in LAMMPS using read_data command.

But if <100> direction is oriented to the z axis of simulation box the dislocations disappear and crystal formed seems perfect.i.e.

lattice bcc ${alat} origin 0.0 0.0 0.0 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
Why is it so? And how can I remove this error.

Anuradha

2

You have to watch out for the dimensions of your simulation cell being commensurate with the lattice orientation.
for a <100> orientation you get correct periodic replication with a single cell (or any combination of lattice units), but if you start rotating the lattice, you may need 2 or more unit cells per direction to get correct periodic replication. example: if the lattice is rotated by 45 degrees, you need 2, if it is rotated by 60 or 30 degrees you need 3. thus the number of lattice units in that direction has to be divisible by that number.

axel.