[QE-users] difference between the internal PBE and the libxc one

[Fabrizio Ferrari Ruffino]

Hello,
there is a bug in QE version 7.2 for exchange_only functionals in libxc, that has been fixed in the develop version.
If you do not want to download the develop branch, tou just have to add the two following lines:

  *   xcoef=1.d0
  *   if (ishybrid .and. exx_started .and. exx_fraction>0.d0) xcoef=1.d0-exx_fraction

at line 355 of XClib/xc_wrapper_gga.f90 and then recompile.
Cheers,
Fabrizio

CNR IOM

________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Ayoub Aouina <ayoubaouina at outlook.com>
Sent: Thursday, August 10, 2023 9:28 PM
To: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
Subject: [QE-users] difference between the internal PBE and the libxc one


Dear all,

I'm currently facing an issue with the use of Libxc for PBE calculations in Quantum ESPRESSO. I'm noticing a significant discrepancy in results when comparing the internal PBE functional (input_dft = "PBE") to using Libxc with the PBE functional (input_dft = "XC-000I-000I-101L-130L-000I-000I").

  *   For internal PBE: Total energy contribution from xc is -4.83542517 Ry.
  *   For Libxc PBE (input_dft = "XC-000I-000I-101L-130L-000I-000I"): Total energy contribution from xc is -0.63113373 Ry.

I'm reaching out to seek insights into why such a substantial difference might occur between these calculations. I wonder if there are specific external parameters that need to be set when utilizing the PBE functional from Libxc.

I would also like to ask why the xc contributions are not printed in the output file for some hybrid functionals like : B3LYP?

Attached is my input file and the pseudo-potential file for a Silicon calculation. Any guidance or recommendations would be highly appreciated.

Best regards,

--
Ayoub Aouina, PhD.,
Institut für Festkörpertheorie und -optik
Friedrich-Schiller-Universität Jena
Max-Wien-Platz 1
07743 Jena
Germany

Mail: ayoub.aouina at uni-jena.de<mailto:ayoub.aouina at uni-jena.de>
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