[QE-users] LIBXC versus internal QE functionals

[Paolo Giannozzi]

On 5/26/24 23:20, Abdesalem Houari via users wrote:

> After checking well the exchange-correlation document 
> (Modules/funct.f90), my first issue seems resolved.

and the second as well: absolute energies depend upon the pseudopotentials

Paolo

> I found that "pbe"   = "sla+pw+pbx+pbc" (= 
> XC-001I-004I-003I-004I-000I-000I).
> So the true PBE needs, not only "pbx" exchange + "pbc" correlation, but 
> also "sla" exchange + "pw" correlation.
> 
> Thanks.
> 
> A. Houari
> 
> 
> On Sunday, 26 May 2024 at 08:54:24 pm GMT+1, Abdesalem Houari via users 
> <users at lists.quantum-espresso.org> wrote:
> 
> 
> Dear All,
> 
> I wanted to do a calculation test using PBE-functional from LIBXC and 
> compare it to the internal QE one. As a test, I opted for body centered 
> cubic (bcc) iron.
> 
> I'm a bit puzzled by the differences in the results.
> 
> - First, for PBE from LIBXC, following the QE user-guide on how to use 
> LIBXC, I put the following input: 
> *input_dft='XC-000I-000I-101L-130L-000I-000I*'. I obtained a total 
> energy value of -39.08694619 Ry.
> 
> - Then, for QE internal PBE functional, after having a look to 
> Modules/funct.f90 file, I deduced the PBE should be forced from the 
> input as follow:**input_dft='XC-000I-000I-003I-004I-000I-000I*'.* Here I 
> was quite surprised  obtaining a different value of the total energy 
> -31.22123378 Ry... It seems like it is not the correct PBE ?
> 
> - When I just use NC-PP (Fe.pbe-mt_fhi.UPF) without forcing the 
> input_dft, I get a similar result to LIBXC-PBE ... The same result is 
> obtained also when I forced the input_dft, but including LDA-exchange 
> (Slater)+correlation (PW) i.e. 
> **input_dft='XC-001I-004I-003I-004I-000I-000I*'*
> *
> *
> I'm really confused ! I**would be grateful if some could give a bit of 
> explanation, on how the input_dft works exactly ? especially with 
> respect to the Module/funct.f90 file which gives all the internal 
> functionals.
> 
> 
> I would also ask for another issue. It is explained in the PW manuel 
> that input_dft overrides the PP. Normally, if I'm not wrong, whatever 
> the kind of the PP given in the input file (PBE or other; 
> norm-conserving or ultra-soft or PAW potential), the code will discard 
> it and does not look at it at all when input_dft is forced.
> Here also I'm confused, I forced the input_dft as: 
> **input_dft='XC-001I-004I-003I-004I-000I-000I*'*, with two different PP 
> (Fe.pbe-mt_fhi.UPF and Fe.pbe-spn-rrkjus_psl.0.2.1.UPF); and the total 
> energies are completely different ! *
> *
> *
> *
> Thanks a lot in advance*
> *
> 
> Sincerely yours.
> 
> 
> ========================================
> Dr. Abdesalem HOUARI
> -------------------------------------------------------------------------------------------
> Department of physics, Theoretical Physics Laboratory
> University of Bejaia-06000. Algeria.
> E-mail: abdeslam.houari at univ-bejaia.dz & habdslam at yahoo.fr
> https://sites.google.com/site/houariabdeslam/homepage 
> <https://sites.google.com/site/houariabdeslam/homepage>
> ========================================
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> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine Italy, +39-0432-558216