Features/improvements for upcoming version v0.4 #48
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Hello all, Firstly, it might be advantageous to be able to dump all output parameters and optimisation functions into a separate output file? I have some intuition telling me that many of the outputs might be very limited, and that the parameters could be clustered around several values. It could be a very long file, but i do believe it could be useful. Secondly[defunct], might it be possible, as the above comment notes, to include the 'which' functionality into the input files that don't include .cif inputs. It is not specified that this should be for only the .cif files, but I would like to completely discount one sublattice from my optimisation. Edit: I have realised that it was a mistake with my formatting of the input file. |
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Hi! |
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Dear maintainer. Thanks for your great work in providing another way to build structures with SQS. In my preliminary test (TiAlN and TiAlN-based systems with B1-NaCl structure), both the calculated energy and the variation trend of elastic constants for the two kinds of structures (sqsgen and ATATsqs) are in accordance. However, the structures built by sqsgen may be a little bit 'brittle' than those built by ATATsqs and the results in the literature holistically. Although I think it will not influence the correctness of the calculation results as long as all the structures were built in the same way. I'm concerned it may be attributed to my YAML input, especially the setting for shell_weights, or it is just a systemic influence. And is there any advice on how to adjust the shell_weights, or is it well enough to choose the default values? Thanks a lot for your excellent project. Here is my YAML input and test results: |
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Dear Chris,
May you please expand a bit on what do you mean by “being brittle”?
Thanks,
David
…On Sat 26. Jul 2025 at 12:51, dgehringer ***@***.***> wrote:
Hi @SR333Chris <https://github.com/SR333Chris>!
Many thanks for your interest in the program.
I have to admit that I myself was not a ATAT user, while I have heard a
lot of it and people in my former working group used it also.
Given that I am not 100% sure on what ATAT actually does. However, let me
give you some context on the snippet you have where the parameter
"prefactors" and "prefactor_mode" are set.
Basically there are two ways of thinking when doing such an optimisation:
1.
You think of the whole structure as a single whole structure and then
you optimize all SRO parameters in your case (leaving aside same atoms pair
bonds) Al-Ti, Al - N and Ti - N. If this is your intent I would suggest to
remove the "prefactors" and "prefactor_mode"
2.
Or you say will only the atoms at the metal sub lattice mix and I do
not care and I do not care about species sitting on the Nitrogen sub
lattice. In this you'd optimize only Al-Ti bonds. You do not care about Al
- N bonds, Ti - N bonds. Then I suggest to again to remove "prefactors" and
"prefactor_mode" and set which: Ti and remove the Nitrogen section from the
composition.
It depends a little bit agains what you compare it to.
"prefactor_mode" came from the restriction that one could only optimize
one sub lattice at a time. If you wanted to optimize more sub lattices
(assuming that do not interact with each other) in a single run. E.g. if
you wanted to create e.g. TiN -> (Ti,Al)(Cr,N) this parameter were
introduced. This was a possible way to do it however, it had some flaws,
namely this strange setting of the "shell_weights"
In the upcoming version I have introduced sub lattice "modes" namely that
address exactly this issue. Those are called *interact* which corresponds
to 1.) and *split* which corresponds to 2.)
pre-release pip wheels are already available, I'm still fighting with the
conda CI.
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Dear Chris,
While I am happy you could resolve your concerns, I do not understand it
scientifically: how could you have elastic constants in accordance, but not
the B/G (which are calculated from Cij)?
Best wishes,
David
…On Fri, 1 Aug 2025 at 10:07, SR333Chris ***@***.***> wrote:
Dear David,
The "brittle" comes from the calculated semi-empirical indicator B/G and
Cauchy Pressure values by the stress-strain method. I guess it may be
attributed to more Al-Al interaction in the structures formed based on my
previous setting. However, after I adjusted the input file as suggested by
@dgehringer <https://github.com/dgehringer>, the current calculated
results are much closer to structures built by ATAT.
Thanks,
Chris
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Can you be a bit more specific about what "a bit different" means? There
will always be some dependence on the actual SQS, and even within the SQS,
there will be differences between $x$, $y$, and $z$ directions. There are, of
course, unphysical effects caused only by the small size of the used
cell, and become pronounced in particular for tensorial properties such as
elastic constants. We have discussed this issue in this
paper: [10.1103/PhysRevB.90.184106](https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.184106)
David
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Personally, I would not be concerned so much about the 10 GPa difference,
which is about 5%. As a test, try to generate several SQSs and get C44 for
those. What is the spread, then? My guess would be that it can easily be in
the same range, although all structures have the same SRO.
Another point for consideration: How much does C44 differ from C55 and C66?
Best regards,
David
…On Fri, 1 Aug 2025 at 12:58, SR333Chris ***@***.***> wrote:
The 'bit difference' is mainly about the difference in C44 (215.892 and
203.505 for Ti0.5Al0.5N by two kinds of structures, respectively, based on
my previous input setting).
Thanks a lot for introducing your paper to help me further study it! I can
get the influence of cell size by browsing through this paper; however, I
need a little time to read it intensively to understand it as fully as
possible.
Best wishes,
Chris
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Hang on - how can you restrict the symmetry when generating the SQS? I
think this is not possible with the current version of sqsgenerator.
So, the correct way of calculating the elastic constants is to calculate
the full matrix of elastic constants (6x6 Cij matrix) and then to project
it on the desired symmetry (10.1007/s10659-006-9082-0). This, for the cubic
system, means averaging:
C11(B1) = (C11 + C22 + C33)/3
C44(B1) = (C44 + C55 + C66)/3
David
…On Fri, 1 Aug 2025 at 13:56, SR333Chris ***@***.***> wrote:
Thank you for your suggestions. Actually, I was more concerned that there
was something wrong with my input file at the beginning, rather than the
slight difference, and @dgehringer <https://github.com/dgehringer> has
helped me to resolve it. The little difference is acceptable, and I also
agree that it can easily be in the same range as long as all structures
have the same SRO.
Due to I have restricted the symmetry of all the structures to space group
225 (B1 structure) during calculation, the C55 and C66 haven't been
calculated.
Thanks,
Chris
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👋 Hello everyone
I currently plan to give sqsgen a major rewrite. While most the changes should go unnoticed by users, the rewrite will involve architectural 🏗️ changes to the core library.
Therefore, I thought it would be a good to ask users for their, feedback, feature wish list and enhancement suggestions.
📬 If you know someone who uses sqsgenerator, please forward this page
💡 Please post your ideas for enhancements below (framework integration, custom objectives?, output formats, HDF?, etc., run it as a service) whatever comes to your mind
Here's a list of planned tasks:
🔈 Feel free to post your suggestions and ideas so that we can discuss them
👥 If you want to (or possibly you know someone who wants to) contribute also with your code, please do not hesitate to contact me
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