[QE-users] HSE XC - mismatch between energy- and force-minimizing bond length for H2 and O2

[Robert Wexler]

Dear Tobias,

Thank you for your quick and helpful response!

Best regards,
Rob
---------------------------------------------
Robert B. Wexler, PhD
University of Pennsylvania, 2019
rwexler at sas.upenn.edu
(215) 801-8741
---------------------------------------------



On Mon, May 13, 2019 at 11:52 AM Tobias Kloeffel <tobias.kloeffel at fau.de>
wrote:

> Dear Robert Wexler,
>
> there are some additional force terms when using Vanderbilt Ultrasoft
> pseudopotentials in HFX calculations. These are not implemented, and using
> a more recent QE version will actually stop, because these force terms are
> missing.
>
> Regards,
>
> Tobias Klöffel
>
> On 5/13/19 5:33 PM, Robert Wexler wrote:
>
> Dear QE users,
>
> I obtained some perplexing results using the HSE XC functional that I
> would like to share with you.
>
> I calculated the ground state potential energy surfaces of H2 and O2 as a
> function of bond length strain (i.e. % different from some arbitrary
> starting bond length). The results are attached in this email as
> "h2-compare-force-energy.pdf" and "o2-compare-force-energy.pdf",
> respectively. The right panel for H2 and O2 shows the total energy as a
> function of bond length strain. As you can see, a slight contraction of the
> original bond length is preferred. If you look at the left panel, however,
> the total force is minimized at positive strains of greater magnitude. The
> minimum force and total energy should occur at the same bond length strain,
> which could present some problems for geometry optimization. I have
> attached inputs and outputs for each calculation in .tar.gz files
> ("h2-qe-in-out.tar.gz" and "o2-qe-in-out.tar.gz").
>
> I took this one step further and tried to relax a water molecule using HSE
> and found that the relaxation does not converge. This can be seen in
> "h2o-hse-relax.pdf". As the BFGS proceeds, it cannot converge because one
> configuration decreases the total energy (steps 1, 4-12, 15-16) and another
> decreases the total force (steps 2-3, 13-14).
>
> Here is a quick summary of my computational resource and QE settings:
> - Cori, NERSC, KNL
> - QE 6.3
> - GBRV PSPs
> - SCF calculation
> - 35/350 Ry cutoffs
> - LSDA for O2 (I get the correct total/absolute spin magnetization of the
> O2 molecule)
> - HSE, 1x1x1 q-grid
> - Assume isolated, "mt"
> - Gamma point
> - More details can be found in the inputs and outputs I've supplied
>
> Thank you in advance for any help you can provide.
>
> Best,
> Rob
> ---------------------------------------------
> Robert B. Wexler, PhD
> University of Pennsylvania, 2019
> rwexler at sas.upenn.edu
> (215) 801-8741
> ---------------------------------------------
>
>
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>
> --
> M.Sc. Tobias Klöffel
> =======================================================
> Interdisciplinary Center for Molecular Materials (ICMM)
> and Computer-Chemistry-Center (CCC)
> Department Chemie und Pharmazie
> Friedrich-Alexander-Universität Erlangen-Nürnberg
> Nägelsbachstr. 25
> D-91052 Erlangen, Germany
>
> Room: 2.305
> Phone: +49 (0) 9131 / 85 - 20423
> Fax: +49 (0) 9131 / 85 - 26565
>
> =======================================================
>
> E-mail: tobias.kloeffel at fau.de
>
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