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Unable to open bandgap of FeO (GGA+U & HSE06)

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sukhito teh:
Dear Staffs and Users,
I noticed that both GGA+U and HSE06 failed to open the bandgap of FeO. FYI, calculations with VASP can have similar issue, but those can usually be solved by turning off the K-Points symmetry. However,  even if I am setting use_symmetries  = False in AlgorithmParameters, the calculation still assume time reversal symmetry, so I am not sure if similar approach would solve the problem. May I know if there is any suggestion to solve this problem?
Thank you for your time.

best regards,
Sukhito

Anders Blom:
The keyword you are looking for is force_timereversal=False (https://docs.quantumatk.com/manual/Types/MonkhorstPackGrid/MonkhorstPackGrid.html)

sukhito teh:
Thank you for your reply. I tried rerun with this setting, but it doesn't seem to work.

Anders Blom:
Define "doesn't work". The calculation ran fine and I don't any density of states being calculated so how can you tell there is no band gap?

You might want to try the Dielectric Dependent Hybrid model as discussed in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8007096/ where FeO is an included example. This model is available QuantumATK using

exchange_correlation = HybridGGA.HSE06DDH

(cf. https://docs.quantumatk.com/manual/DFTLCAO.html#dielectric-dependent-hybrid-functionals)

sukhito teh:

--- Quote from: Anders Blom on June  8, 2023, 20:53 ---Define "doesn't work". The calculation ran fine and I don't any density of states being calculated so how can you tell there is no band gap?

You might want to try the Dielectric Dependent Hybrid model as discussed in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8007096/ where FeO is an included example. This model is available QuantumATK using

exchange_correlation = HybridGGA.HSE06DDH

(cf. https://docs.quantumatk.com/manual/DFTLCAO.html#dielectric-dependent-hybrid-functionals)

--- End quote ---

I am so sorry that I didn't make it clear in my previous reply, doesn't work refer to unable to turn off the time reversal symmetry. Anyway, I tried few more approaches and these are the summary:
1. Using SG15 basis + PBEU --> no Band Gap
2. USing SG15 basis + HSE06 --> no Band Gap
3. Using Dojo basis +HSE06 --> no Band Gap
4. Using Dojo basis + DDH --> no Band Gap
5. Using Dojo basis + local DDH --> no Band Gap
6. Using Dojo basis + local DDH + ADMM --> band gap open!

I am not sure what is the explanation for this, but I am really thankful for your help. The ADMM is interesting, it speeds up the calculation for more than 10 times (per step), although it takes much larger steps to converge. Have a nice day!

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