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
[email protected] <mailto:[email protected]>
(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: [email protected]
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Quantum Espresso is supported by MaX (www.max-centre.eu/quantum-espresso)
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