[QE-users] Problem with computed bandgap

[AISWARYA CHANDRAN]

Dear Lorenzo,

Thank you very much for your response and for sharing the details regarding
your study on Ce₂O₂S. I tried using the same high-precision Ce
pseudopotential (Ce.pbe-spdfn-rrkjus_psl.1.0.0.UPF) from the PSLibrary, but
unfortunately, I wasn't able to reproduce the results you mentioned.

If possible, could you please share the input files you used? That would be
extremely helpful for me to understand the setup and ensure I am not
missing anything crucial.

Thanks again for your support!



*Thanks and with Regards, *
*Aiswarya Chandran*

*Research Scholar*

*Laboratory for Advanced Materials and Applied Research*
*Department of Chemistry*
*NIT Calicut, Kerala, India, 673 601*

On Mon, 30 Jun, 2025, 12:44 am Lorenzo Paulatto, <lorenzo.paulatto at cnrs.fr>
wrote:

> Hello,
>
> when studying the similar compoiunf Ce2O2S, I only had good results usign
> the high-precision Ce pseudopotential Ce.pbe-spdfn-rrkjus_psl.1.0.0.UPF
> from the pslibrary that includes 5s5p6s4d5d4f in valence (22 electrons in
> valence) and requires a ridiculous 200 Ry cutoff to converge, despite being
> Ultrasoft. The U was almost 7eV. You can find more details in this paper
> and its supplementary materials :
> https://pubs.acs.org/doi/abs/10.1021/acs.chemmater.9b00450 (I can send
> the inout files if you want)
>
> hth
> On 29/06/2025 18:55, AISWARYA CHANDRAN via users wrote:
>
> Dear Quantum ESPRESSO developers and users,
>
> I am working on Ce₂O₃ and trying to reproduce the experimentally reported
> band gap (~2.4–2.7 eV) using LDA+U in combination with spin–orbit coupling
> (SOC) in Quantum ESPRESSO. However, despite using U = 6 eV and including
> SOC via fully relativistic pseudopotentials, the computed band gap is
> significantly underestimated (around 1.1 eV).
>
> Here are the key points of my setup:
>
> - Code version: QE 7.X
> - Pseudopotential: Ce.pz-spdfn-rrkjus_psl.1.0.0.UPF (fully relativistic)
> - Functional: PZ-LDA
> - Hubbard_U applied: U = 6.0 eV on Ce 4f
> - Calculation type: SCF → bands
>
> - Structure: 5-atom primitive cell from literature (a = 3.87 Å, c/a =
> 1.522)
> - `nbnd = 41`
> - Gap is computed using `bands.x` and visual inspection
>
> Despite these, the gap remains ~1.1 eV. Literature reports higher values
> for similar setups. I also observe that relaxing the cell via `vc-relax`
> makes the lattice smaller, which further reduces the gap. Using
> experimental lattice constants does help, but not enough to reach the
> expected values.
>
> Could you please advise on:
> 1. Whether this pseudopotential is appropriate for SOC + LDA+U
> calculations on Ce?
> 2. Any suggestions on correcting the band gap underestimation?
> 3. Whether a better suited pseudopotential or approach (e.g., using GGA+U,
> HSE, etc.) is recommended? I am attaching the input file
> 4. I tried the same with Ce.pz-spdn-rrkjus_psl.1.0.0.UPF it gives band gap
> of 3.7 eV. shall i proceed with spdn?
>
> I would greatly appreciate your insights.
>
>
> --
> *Thanks and with Regards, *
> *Aiswarya Chandran*
>
> *Research Scholar *
>
> *Laboratory for Advanced Materials and Applied Research *
> *Department of Chemistry*
> *NIT Calicut, Kerala, India, 673 601*
>
> _______________________________________________________________________________
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>
> --
> Dr. Lorenzo Paulatto
> IR IMPMC - CNRS UMR 7590 / Sorbonne Université / MNHN
> phone: +33 (0)1 442 79822 / telegram: lpaulatto
> http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
> 23-24/423 B115, 4 place Jussieu
> <https://www.google.com/maps/search/4+place+Jussieu?entry=gmail&source=g>
> 75252 Paris CX 05
>
> _______________________________________________________________________________
> The Quantum ESPRESSO Foundation stands in solidarity with all civilians
> worldwide who are victims of terrorism, military aggression, and
> indiscriminate warfare.
>
> --------------------------------------------------------------------------------
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