Dear ATAT Community,
I am trying to get random structures by doping ‘Mn’ in ‘Fe’ sites in my rndstr.in file by constructing a [2 2 1] super cell and limiting the dopant atom from 1 to 5 atoms in the supercell. But the jobs were terminated very soon after I hit the submit command and no random structures were outputted. I was able to run the command and get the random structures with the same input files for doping in a step of 4 and 2 atoms per supercell. What has gone wrong - could you please suggest?
For more information, please see the attached rndstr.in and sqscell.out files I used.
The answer to my questions is highly appreciated. Thank you.
You should run the command in a way that you can see the error message output. I suspect it was "Impossible to match point correlations due to incompatible supercell size."
You are requesting a composition that is probably impossible to achieve in the specified cell size.
(It’s a composition which, when written as a fraction, has a large denominator).
Dr. van de Walle,
Thank you for the reply. I had got exactly the same error message output. I didn’t make it clear in my original post that I understood the error message, and that is not the problem here.
Below is an input rndstr.in for the 1 Mn doped SQS:
-2.848146 2.848146 3.115553
2.848146 -2.848146 3.115553
2.848146 2.848146 -3.115553
1.000000 0.000000 0.000000
0.000000 1.000000 0.000000
0.000000 0.000000 1.000000
0.250000 0.750000 0.500000 Fe=.96875000000000000000,Mn=.03125000000000000000
0.294232 0.294232 0.000000 Fe=.96875000000000000000,Mn=.03125000000000000000
0.705768 0.705768 0.000000 Fe=.96875000000000000000,Mn=.03125000000000000000
0.757186 0.757186 0.514372 Fe=.96875000000000000000,Mn=.03125000000000000000
0.757186 0.242814 0.000000 Fe=.96875000000000000000,Mn=.03125000000000000000
0.242814 0.757186 0.000000 Fe=.96875000000000000000,Mn=.03125000000000000000
0.242814 0.242814 0.485628 Fe=.96875000000000000000,Mn=.03125000000000000000
0.750000 0.250000 0.500000 Fe=.96875000000000000000,Mn=.03125000000000000000
0.000000 0.000000 0.000000 N
and I am using a super-cell in sqscell.out:
1
2 0 0
0 2 0
0 0 1
to have a total of 84 = 32 exchangeable sites in my super-cell.
As you can see from above rndstr.in that the Mn has a fractional composition of .03125 which gives .0312532=1. The SQS generation only worked for 4 Mn doping while I got the above error message for other remaining four (1,2,3,5) Mn doping.
The issue is a bit more subtle when your atomic sites are not symmetrically equivalent.
The output file
rndstrgrp.out
groups equivalent site together.
To satisfy the definition of a SQS, the composition within each group of equivalent site must match the requested composition.
Satisfying this typically requires a larger supercell than if you only have one type of sites.
You could manually force each group of site to have a simpler (fraction with smaller denominator) composition that averages to the desired composition, if you really want a smaller cell.