I am attempting to use mcsqs to generate a SQS of a perovskite which has an A-site cation sublattice ordered between two species, a single species occupying the B-site, and an anion sublattice that is disordered between two species.
The two pieces of relevant information I’ve found are
-
The help for corrdump, which says "When only one symbol is listed, this site is ignored for the purpose of calculating correlations, but not for determining symmetry."
-
An excerpt from Efficient Stochastic Generation of Special Quasirandom Structures which says "All symmetry equivalent sites must also have the same occupations. To override this requirement, `dummy’ species (with zero occupation) that differ in the two sublattices must be included."
In my first attempt, I described two different A-site cations as shown
3.933290 0.000000 0.000000
0.000000 3.933290 0.000000
0.000000 0.000000 7.565200
1.000000 0.000000 0.000000
0.000000 1.000000 0.000000
0.000000 0.000000 1.000000
0.500000 0.000000 0.250000 O=0.83333,F=0.16667
0.500000 0.000000 0.750000 O=0.83333,F=0.16667
0.500000 0.500000 0.000000 O=0.83333,F=0.16667
0.500000 0.500000 0.500000 O=0.83333,F=0.16667
0.000000 0.500000 0.250000 O=0.83333,F=0.16667
0.000000 0.500000 0.750000 O=0.83333,F=0.16667
0.000000 0.000000 0.000000 Ba
0.000000 0.000000 0.500000 Y
0.500000 0.500000 0.250000 Fe
0.500000 0.500000 0.750000 Fe
However, it ignored the cations altogether when finding clusters, only considering anion-anion interactions. I then attempted
0.000000 0.000000 0.000000 Ba=1,Y=0
0.000000 0.000000 0.500000 Y=1,Ba=0
0.500000 0.500000 0.250000 Fe=1,La=0
0.500000 0.500000 0.750000 Fe=1,La=0
using "dummy" species to override the symmetry requirement. This failed with the error message
"Please drop irrelevant species when site is fully occupied with one species", so I tried
0.000000 0.000000 0.000000 Ba=1,Mn=0
0.000000 0.000000 0.500000 Y=1,La=0
0.500000 0.500000 0.250000 Fe
0.500000 0.500000 0.750000 Fe
which failed with the same message. What is the correct way to specify this structure so that it recognizes the A-site (Ba and Y) is ordered, and considers Ba-O, Ba-F, Y-O, and Y-F clusters to be four separate categories?