[QE-users] vc-relax with PBE0 and QE6.7

Thu Jan 21 22:51:02 CET 2021

Dear Lorenzo and Giuseppe,

Thanks for the tips.

Indeed ecutfock = ecuwfc doesn't add significant error in energy convergence for my system (+0.1 meV/atom).

Then I changed the k-point grid from 3x2x3 to 2x1x2. 3x2x3 was perfectly converged for my system, and switching to 2x1x2 doesn't add significant error either (-0.1 meV/atom).

As a result, the scf calculation (keeping the same convergence parameters) with PBE0 is now only 5 times as long as PBE. With a very little trade-off, I think.

Thanks again!
Xavier

________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
Sent: Thursday, January 21, 2021 9:56 AM
To: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] vc-relax with PBE0 and QE6.7

Dear Xavier
Lorenzo is totally right, but there are two further parameters that
can improve your experience with exact-exchange functionals in QE:

1) ecutfock

The cutoff for nonlocal integrals has a huge impact on computational
resources. The default is ecutfock=ecutrho, but you rarely need that.
In my experience, ecutfock=ecutwfc is quite satisfactorily for
geometry optimizations, and ecutfock=1.5~2*ecutwfc is a sensible
choice for properties calculation. You can test it on a small system.

2) adaptive_thr=.true.

In systems having no particular scf convergence issues, this generally
provides a speedup of inner scf loops.

HTH
Giuseppe

Quoting Lorenzo Paulatto <paulatz at gmail.com>:

> Yes. It mostly depends on the choice of nq1x, nq2x and nq3x.
> Local-density is linear in the number of k-points, but exact
> exchange is quadratic, and it can get slow very quickly
>
> Lorenzo Paulatto - Paris
> On Jan 21 2021, at 4:14 pm, Bidault, Xavier <xavbdlt at uic.edu> wrote:
>>
>> Thank you, Giuseppe. I tried with ONCV SG15 PP library and it went
>> fine. However I wasn't expecting PBE0 to be so much longer than PBE
>> for the same calculation. I don't have yet the whole convergence
>> curve w.r.t. cutoff, but with the same convergence parameters, same
>> k-point grid... PBE0 is 300-400x slower than PBE for an SCF
>> calculation. Is it the right order of magnitude?
>>
>> From: users <users-bounces at lists.quantum-espresso.org> on behalf of
>> Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
>> Sent: Wednesday, January 20, 2021 6:22 AM
>> To: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
>> Subject: Re: [QE-users] vc-relax with PBE0 and QE6.7
>>
>>
>>
>> Dear Xavier
>> Forces can be calculated in the case of PBE0 and other hybrid EXX
>> functionals if you use norm-conserving (NC) pseudopotentials. No,
>> there is no way to perform calculations without pseudopotentials in QE.
>> HTH
>> Giuseppe
>>
>> Quoting "Bidault, Xavier" <xavbdlt at uic.edu>:
>> > Hello,
>> >
>> > I would like to run a geometry optimization (vc-relax) using PBE0
>> > and QE6.7. I got the following error message:
>> > Error in routine setup (1):
>> > forces for hybrid functionals + US/PAW not implemented
>> >
>> >
>> > I guess this means I have to rely on another software, don't I? Or
>> > is there a way to discard the need of PP with PBE0 and QE6.7?
>> >
>> > Thank you,
>> > Xavier
>>
>>
>>
>> GIUSEPPE MATTIOLI
>> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
>> Via Salaria Km 29,300 - C.P. 10
>> I-00015 - Monterotondo Scalo (RM)
>> Mob (*preferred*) +39 373 7305625
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>> E-mail: <giuseppe.mattioli at ism.cnr.it>
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>

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