Strange crystal structure in mp-1068462

I found a strange crystal structure:
It is LaS with incredibly huge lattice (e.g. c_len = 90.953 Å).
I have searched the Web for a while, I could not find other paper or resources that reporting this material.

I am not sure for this material but would like to notice you just in case it is inaccurate.

Thank you.

Hi @resnant, welcome.

Yes, this structure is indeed strange, we have a few “bad” structures on Materials Project. However, the important thing is that these structures are correctly identified as being very high energy. See the “Energy Above Hull” on that page of 2.669 eV / atom – this is exceptionally high. Most synthesizable materials are below around 0.2 eV/atom.

Materials Project is a computational database, we calculate crystals from experimental sources like the ICSD, but also structures that users have submitted or from other projects, some of which are very high energy. These calculations are automated, and we don’t know before calculating them if they will be very unstable or not. Once published, we consider it bad form to “delete” a material even if it is very unstable, since someone may already have referenced it. The important thing is to consult the predicted energies above hull when performing a search.

In future, it’s likely many of these materials will be deprecated, meaning that the data will remain available but they will not show up in search results by default.



Thank you, @mkhorton for a response.

This explanation makes a lot of sense to me. So this is an example of an unstable structure.

the important thing is that these structures are correctly identified as being very high energy.

I was a bit confused because I am an experimental scientist and have never encountered such a structure in my study.

Thanks a lot.

Yes, this is an example of a very unstable structure :slight_smile: Glad it helped! From an experimental point of view, you want to look at structures with an “energy above hull” below 0.2 eV/atom, some chemistries can tolerate higher (0.5 eV/atom), especially under non-equilibrium growth conditions, but beyond that is exceptionally rare. Typically, when we do a screening we look at materials in the 0 to 0.05 eV/atom range.

This paper, Thermodynamic limit for synthesis of metastable inorganic materials, is a good overview of what a sensible limit of metastability might be for different chemistries.

Wow, thank you for your additional advice and the literature. The paper seems very interesting to me, and I will check it!

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