Regarding SQS of ZnS

Alloy Theoretic Automated Toolkit (ATAT)
1

Dear ATAT users,
I was trying to generate a SQS for ZnS Cubic structure using mcsqs, implemented in ATAT code. In parent material ZnS, Zn site has random distributions of Cu and In. I started my calculations with

rndstr.in
1 1 1 90 90 90
0 0.5 0.5
0.5 0 0.5
0.5 0.5 0
0.0000000000 0.0000000000 0.0000000000 Cu=0.5, In=0.5
0.2500000000 0.2500000000 0.2500000000 S

But at the end of calculations, there is a phase transition in structure. I was expecting that I would get cubic structure but I did not get cubic structure. Could someone please suggest and comment ? Is it possible to have structure phase transition after random distribution in ZnS?

For more information, I have below POSCAR (64 atoms) file at end of calculations:
POSCAR
xxx
1.00000000 -0.50000000 2.50000000
-1.00000000 -0.50000000 2.50000000
0.00000000 -1.50000000 -0.50000000
Cu In Se
16 16 32
Direct
0.87500000 0.87500000 0.75000000
0.93750000 0.93750000 0.37500000
0.46875000 0.96875000 0.18750000
0.75000000 0.75000000 0.50000000
0.81250000 0.81250000 0.12500000
0.21875000 0.71875000 0.68750000
0.28125000 0.78125000 0.31250000
0.56250000 0.56250000 0.62500000
0.09375000 0.59375000 0.43750000
0.50000000 0.50000000 1.00000000
0.71875000 0.21875000 0.68750000
0.25000000 0.25000000 0.50000000
0.31250000 0.31250000 0.12500000
0.59375000 0.09375000 0.43750000
0.65625000 0.15625000 0.06250000
0.12500000 0.12500000 0.25000000
0.34375000 0.84375000 0.93750000
0.40625000 0.90625000 0.56250000
0.68750000 0.68750000 0.87500000
0.62500000 0.62500000 0.25000000
0.84375000 0.34375000 0.93750000
0.90625000 0.40625000 0.56250000
0.96875000 0.46875000 0.18750000
0.03125000 0.53125000 0.81250000
0.15625000 0.65625000 0.06250000
0.37500000 0.37500000 0.75000000
0.43750000 0.43750000 0.37500000
0.78125000 0.28125000 0.31250000
0.18750000 0.18750000 0.87500000
0.53125000 0.03125000 0.81250000
0.06250000 0.06250000 0.62500000
1.00000000 1.00000000 1.00000000
0.03125000 0.78125000 0.56250000
0.09375000 0.84375000 0.18750000
0.50000000 0.75000000 0.75000000
0.56250000 0.81250000 0.37500000
0.62500000 0.87500000 1.00000000
0.84375000 0.59375000 0.68750000
0.90625000 0.65625000 0.31250000
0.96875000 0.71875000 0.93750000
0.37500000 0.62500000 0.50000000
0.43750000 0.68750000 0.12500000
0.71875000 0.46875000 0.43750000
0.78125000 0.53125000 0.06250000
1.00000000 0.25000000 0.75000000
0.06250000 0.31250000 0.37500000
0.12500000 0.37500000 1.00000000
0.18750000 0.43750000 0.62500000
0.25000000 0.50000000 0.25000000
0.31250000 0.56250000 0.87500000
0.53125000 0.28125000 0.56250000
0.59375000 0.34375000 0.18750000
0.65625000 0.40625000 0.81250000
0.87500000 0.12500000 0.50000000
0.93750000 0.18750000 0.12500000
0.34375000 0.09375000 0.68750000
0.40625000 0.15625000 0.31250000
0.46875000 0.21875000 0.93750000
0.68750000 0.93750000 0.62500000
0.75000000 1.00000000 0.25000000
0.81250000 0.06250000 0.87500000
0.21875000 0.96875000 0.43750000
0.28125000 0.03125000 0.06250000
0.15625000 0.90625000 0.81250000

and the lattice constants are:

a b c alpha beta gamma
15.52136 15.52136 8.96126 96.6307 96.6307 42.8334

Thanks and Kind regards

Sandeep

2

The sqs for a lattice with cubic symmetry does not need to have a cubic cell.

3

Dear Prof. Axel van de Walle,

Thanks for your reply. Could you please explain the reason for this phase transition in SQS?

kind regards

Sandeep

4

It’s not a phase transition.
In general, a supercell extracted from a random solid solution will not have the symmetry of the underlying lattice. It’s local symmetry is broken by the random occupations.

5

Dear Prof. Axel van de Walle,

Many thanks for your explanation. I was also thinking same reason.

kind regards

Sandeep