Omega phase

Alloy Theoretic Automated Toolkit (ATAT)
1

Dear All,

I am trying to make SQS using mcsqs for Omega phase of Ti-Al-V alloy. I am not getting the correct unit cell description by rndstrgrp.out. My rndstr.in file is:
1 1 0.353147 90 90 60
1 0 0
0 1 0
0 0 1
.0 .0 .0 Ti=0.925925926, Al=0.037037037, V=0.037037037
.333333 .333333 .5 Ti=0.925925926, Al=0.037037037, V=0.037037037
.666667 .666667 .5 Ti=0.925925926, Al=0.037037037, V=0.037037037

I use the following commad to generate clusters:
corrdump -l=rndstr.in -ro -noe -nop -clus -2=0.79 -3=0.68

Then I use following command to make SQS for 54 atoms:
mcsqs -n 54
It gave following error message:
Impossible to match point correlations due to incompatible supercell size.

The rndstrgrp.out gives:
1.000000 0.000000 0.000000
0.500000 0.866025 0.000000
0.000000 0.000000 0.353147
1.000000 0.000000 0.000000
0.000000 1.000000 0.000000
0.000000 -0.000000 1.000000

0.000000 0.000000 0.000000 Ti=0.925926,Al=0.037037,V=0.037037

0.333333 0.333333 0.500000 Ti=0.925926,Al=0.037037,V=0.037037
-0.333333 -0.333333 0.500000 Ti=0.925926,Al=0.037037,V=0.037037

The motif is not corrctly identified. There should be 1 sub-lattice.

Warm Regards,
Shailendra

2

The space group of omega phase is P 6/m m m. There are two sub-lattices:
0,0,0 (1a)
1/3,2/3,1/2 2/3,1/3,1/2 (2d)

Therefore, the rndstrgrp.out output is correct. I changed the composition of the two sub-lattices such that it gives integer number of atoms for 54 atoms supercell. Now, the code is working.

3

I’m encountering a similar issue for a defect structure with 114 atoms. I tried to use 29/114: 0.25438596491 (this repeats till about 20 decimal places…).

But I ran into the same problem with "impossible to match…"

How did you resolve your example here?

I see you have 50, 2,2 atoms for the species.

4

By default, the code only enforce 1e-5 accuracy, so no need to include so many decimal places.
The problem is more likely that you have symmetrically distinct sublattices. Check the rndstrgrp.out file.