MCSQS for a topological insulator with disorder

Alloy Theoretic Automated Toolkit (ATAT)
1

Hi all,

I am very new to using SQS and not quite sure about where I am making a mistake. My problem is the following:

I am trying to get the bestsqs structure for the topological insulator Bi(1.1)Sb(0.9)Te(2)S. This material consists of quintuple layers (QLs) bound to each other via weak vdW forces. It has disorder in the Bi and Sb layers only, with the occupation of Bi and Sb being 0.53 and 0.47 respectively. For the purpose of running mcsqs, I am using 0.5 as the occupation for both Bi and Sb. The lattice parameters are as follows:

a = b = 4.21 Angstrom
c = 59.1 Angstrom (for 2 Unit cells or 6 QLs; c for 1 Unit cell consisting of 3 QLs is half of this value)
alpha = beta = 90
gamma = 120

I am interested in getting the bestsqs for a slab supercell consisting of 6QLs (consisting of total 30 atoms). I tried running the mcsqs program but looking at the mcsqs.log file, it appears that the code is stuck at the first step itself. I am using the following two commands:

corrdump -l = rndstr.in -ro -noe -nop -clus -2=4 -3=4

mcsqs -n=30 -l=rndstr.in

Please let me know what could be the issue here.

Thanks.

2
  1. maybe remove the spaces in -l = rndstr.in
  2. without your rndstr.in file it’s difficult to debug this.
  3. If it’s stuck at the corrdump step, then try reducing the ranges (now 4) and perhaps eliminate the -3=… option . it could be that the number of clusters is very large.
3

Can you paste your rndstr.in in the message. The upload feature seems to be not working at the moment.

4

Hi

Thanks for your reply. I tried your suggestion, I don’t seem to get any different result. The relevant files are attached. Please let me know what could be the issue here.

Thanks in advance.

5

4.21053 4.21053 59.10904 90 90 120
1 0 0
-0.5 0.866025 0
0 0 1
-0.000000000 -0.000000000 0.195865010 Bi=0.5, Sb=0.5
-0.000000000 -0.000000000 0.304134990 Bi=0.5, Sb=0.5
0.000000000 0.000000000 0.695864946 Bi=0.5, Sb=0.5
-0.000000000 -0.000000000 0.804135054 Bi=0.5, Sb=0.5
0.333333351 0.666666721 0.029198331 Bi=0.5, Sb=0.5
0.333333351 0.666666721 0.137468329 Bi=0.5, Sb=0.5
0.333333351 0.666666721 0.529198333 Bi=0.5, Sb=0.5
0.333333351 0.666666721 0.637468345 Bi=0.5, Sb=0.5
0.666666680 0.333333361 0.362531655 Bi=0.5, Sb=0.5
0.666666680 0.333333361 0.470801667 Bi=0.5, Sb=0.5
0.666666680 0.333333361 0.862531655 Bi=0.5, Sb=0.5
0.666666680 0.333333361 0.970801635 Bi=0.5, Sb=0.5
0.000000000 0.000000000 0.107545000 Te
-0.000000000 -0.000000000 0.392455024 Te
-0.000000000 -0.000000000 0.607545040 Te
0.000000000 0.000000000 0.892454960 Te
0.333333351 0.666666721 0.440878330 Te
0.333333351 0.666666721 0.225788347 Te
0.333333351 0.666666721 0.940878330 Te
0.333333351 0.666666721 0.725788379 Te
0.666666680 0.333333361 0.274211653 Te
0.666666680 0.333333361 0.059121662 Te
0.666666680 0.333333361 0.774211621 Te
0.666666680 0.333333361 0.559121670 Te
0.000000000 0.000000000 0.000000000 S
0.000000000 -0.000000000 0.500000000 S
0.333333351 0.666666721 0.333333355 S
0.333333351 0.666666721 0.833333290 S
0.666666680 0.333333361 0.166666661 S
0.666666680 0.333333361 0.666666710 S

6

First, your cell is not primitive (hence the warning). To find the primitive cell:
cp rndstr.in rndstr2.in
cellcvrt.exe -s < rndstr2.in > rndstr.in
Using the primitive cell allows the code to explore more possible supercells.

Second, this is fairly low symmetry structure, so it is possible that there is no good sqs of size 30.
I increased -n to 60 and it found a sqs that fits all the correlation you specified exactly after a few seconds.