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hi,
I ran calculations for two different initial magnetic structures (containing many atoms) using DFT+U method and predicted the first structure to be more stable by the second one by 0.5 eV. When I ran single point calculations on these structures with HSE, it was the second structure that was more stable (by 0.1 eV) than the the first one. Can someone suggest how to resolve this discrepancy? Should I believe the HSE result, which is using the DFT+U geometry but typically better describes the electronic structure of systems? Is there any HSE flag I should play with to confirm the results?
Thanks in advance.

Hi apple, welcome to DFT! ;-)

Well, since DFT suffers from 'hard to know where you are', it is in my eyes not possible to say a or b is right.
Do you have experiments available which might guide you a bit?

Cheers,

alex

hi Alex,
Thanks for the reply. Yes, the DFT+U results are in agreement with the experimental observations, not the HSE results. Assuming that the geometries (DFT+U and HSE geometries) should not be too different, and the fact that HSE usually captures the electronic structure of systems better that DFT+U, which depends on the choice of U, I am surprised that the HSE results are in disagreement with the experiments. The system is a magnetic oxide and it has metal adsorbates on top. For such systems, is it common to get misleading results with HSE? Is there anything I could do to resolve the issue?
Thanks.

Hi apple,

that sounds like quite a challange. I'd try to start an HSE calculation from the DFT+U structure and wavefunction and see, if it turns out to be more stable than the 'normal' approach fpr HSE (e.g. start from scratch).

Cheers,

alex

hi Alex,
Thanks for the reply. My single point HSE calculations I was referring to earlier were using the converged DFT+U geometry. However, I did not use the DFT+U wavefunctions to start with since I thought they are completely different from those of HSE method. Can we do it this way?
Thanks,
apple