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Origin of correlated isolated flat bands in LK99

arxiv.org

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Re: Origin of correlated isolated flat bands in LK99

#91

Post by cyberax »

dcow wrote: post #80
jacquesm wrote: post #77

Earlier quoted context omitted.

Same molecular structure entirely different crystal lattice. It is the formation that is different not the molecules. C = C. They are technically allotropes: https://en.wikipedia.org/wiki/Allotropy And just like here that's a function of how the bulk carbon got to be formed, under extreme pressure and temperatures or less pressure and temperature. It's the recipe that makes the difference, not the ingredients.

As far as I understand, we're saying the same thing. isomer /'aɪsəmər/ noun a compound that exists in forms having different arrangements of atoms but the same molecular weight I'm using isomer to refer to possible different arrangements of "the LK99 compound". I see you're saying allotropes refers to diamond vs carbon (allotrope referring a single element vs isomer referring to compound). That raises a question, wha…

Isomers are structurally different. Allotropes refer to variations of the same element.

You're looking at the word "polymorph": "(chemistry, geology) Any substance or mineral that forms different types of crystal."

Re: Origin of correlated isolated flat bands in LK99

#92

Post by dcow »

cyberax wrote: post #91
dcow wrote: post #80

Earlier quoted context omitted.

As far as I understand, we're saying the same thing. isomer /'aɪsəmər/ noun a compound that exists in forms having different arrangements of atoms but the same molecular weight I'm using isomer to refer to possible different arrangements of "the LK99 compound". I see you're saying allotropes refers to diamond vs carbon (allotrope referring a single element vs isomer referring to compound). That raises a question, wha…

Isomers are structurally different. Allotropes refer to variations of the same element. You're looking at the word "polymorph": "(chemistry, geology) Any substance or mineral that forms different types of crystal."

Thank you.

Re: Origin of correlated isolated flat bands in LK99

#93

Post by throwawaymaths »

KRAKRISMOTT wrote: post #62
ivalm wrote: post #43

Earlier quoted context omitted.

You have to put in the structure and then it's expensive to do the calculation. The space of possible structures is extremely large. If you have candidates then you can run through them, but you can't just random search through trillions of trillions of candidates.

What are all the material science ML companies doing? This would be a perfect technology demo if they can find the target

The problem is that this stuff is severely nonlinear, and for the raw formula there are not that many degrees of freedom to try. If you get a structure, there is no guarantee it's stable, or accessible by our synthetic techniques.

Obtaining the training data is also likely to be tricky.

Re: Origin of correlated isolated flat bands in LK99

#95

Post by jacquesm »

dcow wrote: post #87
jacquesm wrote: post #85

Earlier quoted context omitted.

An isomer can have different valences but still have the same overall chemical formula. So just for an example (I have no idea how to put a tetrahedron in a comment :) ) a chain of C-C-C-C and C-C=C-C (which you likely can not synthesize) would be an isomer but C-C-C-C in one crystal lattice versus C-C-C-C in another crystal lattice would be allotropes. The carbon in graphite sits in sheets (hence the possibility to…

Just double checking, the definitions I'm finding for allotrope are specific to a single element. allotrope /'ælə,troʊp/ noun a structurally different form of an element I'm having trouble finding allotrope used to refer to different forms of a compound. https://www.differencebetween.com/difference-between-allotro...

Yes, you're right, I should have used a more complex example for an isomer.

Re: Origin of correlated isolated flat bands in LK99

#96

Post by akasakahakada »

bibabaloo wrote: post #30
raziel2701 wrote: post #10

Man, I'm feeling stronger about LK-99 being it. This paper is theoretical and she finds that particular Cu substitutions onto specific Pb atomic sites are key to enabling a band structure that is usually linked to high Tc superconductors. What this means for the more practical minded is that the synthesis of superconducting LK-99 is not trivial and you need to make the appropriate substitutional alloy for this to wor…

If this could be simulated, can you help me understand why we couldn't have used simulation to find promising SC materials to investigate further earlier? Are there just too many permutations to investigate? It seems to my own naive self that if LK99 is the real deal, we mostly just got lucky finding it.

Not an expert but it just happen that my lab is full of DFT folks so I heard a lot about those everyweek. As people above already answered the questions, I gonna talk some extras.

1. Computation cost is large. 1 compute task for a small scale ~100 atoms last about 3 days to 1 week on supercomputer.

2. Search space is hugh. For each composition you can have different atomic (or crystal) structure. And here we are talking doping which means introduce impurities into the molecule. Chemical characteristics differs depending on which atom you swap for the impurity. Sometimes you may want to try all places.

3. Depends on initial values. Sometimes the initial value is just bad that the result is totally unusable, then you have tweak a little bit and throw back to supercomputer. This cycle might happen few times for 1 specific formula and structure.

4. Not 100% accurate. Often the resulting numbers are off by a few % or more which is hugh, compare to experimental results. Reason is that the simulation is not full scale, approximation is here and there to reduce computational cost.

Re: Origin of correlated isolated flat bands in LK99

#97

Post by xbmcuser »

dcow wrote: post #42
pengaru wrote: post #37

Earlier quoted context omitted.

What the simulation is saying though is that it requires some luck, not all the arrangements result in the band structure.

I understand. I'm saying that it's not LK-99 as described, then. Rather, it's something else that needs a more precise specification.

Ah no they called the working prototype LK-99 so if it works it is if it does not then it is not. Instead of what you are saying that it works so is not LK-99.

Re: Origin of correlated isolated flat bands in LK99

#98

Post by fnordpiglet »

TillE wrote: post #2

"However, substitution on the other Pb(2) does not appear to have such sought-after properties, despite being the lower-energy substitution site. This result hints to the synthesis challenge in obtaining Cu substituted on the appropriate site for obtaining a bulk superconducting sample" OK I'm starting to actually believe that LK-99 might be the real deal.

It’s sort of an amazing time. All the things we projected were 30 years out 40 years later and manifesting. The degree of skepticism is high, as should be, but the things we knew were achievable just hard to discover are rapidly unfolding. What falls next?

(N.b., I know I’m displaying unreasonable hubris and it’s still more likely than not an illusion or fabrication, but it certainly feels a lot of long term investments are rapidly coming to a head - AI, space, cancer treatments, aging research, EV, even flying cars and fusion - what a great time to be alive)

Re: Origin of correlated isolated flat bands in LK99

#99

Post by zulmkodr »

bawolff wrote: post #86
cubefox wrote: post #23

It's funny to read all those grammatical mistakes in the abstract. They are probably just not native English speakers, but to me it sounds like they were frantically typing the paper as soon as they finally got results after a 20 hour lab marathon and way too much caffeine. :D

It isn't the prettiest prose i have ever read, but no obvious outright mistakes stick out to me. It doesn't read any worse than the average hn comment.

If only they had a technical writer in their team

Re: Origin of correlated isolated flat bands in LK99

#100

Post by rex_lupi »

yellowcake0 wrote: post #24

There's a lot of optimism in this thread, but does DFT (or any theoretical model really) actually have much predictive value in quantum chemistry? I've always gotten the impression that in this field the proof is in the pudding.

The prof who taught us computational chemistry during masters basically said 90% of published results cannot be trusted and most people in this field don't really know what they're doing. Results can look seemingly good and stil be way off from reality, even for very simple molecules. This is a crystal lattice. I take dft and other computational results with a big grain of salt.
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