[QE-users] vc-relax with PBE0 not converging

[Bidault, Xavier]

Hello again,

This is not really better with grid 3x2x3 (off-centered). See image below. Oscillations are visible on density, not much for pressure (but numbers end up periodic anyway). Pressure remains negative. However pressure oscillation decreases with higher number of k-point (Gamma -> 2x1x2 off centered -> 3x2x3 off-centered), but there is still a large offset.

Note that SCF convergence of this organic crystal w.r.t. k-points is perfectly converged with 3x2x3 off-centered grid and PBE. Increasing the number of k-points for PBE0 may be better, but out of time for me. And my guess is it will not solve the pressure offset.

Concerning adding smearing, I don't see the point. This molecular system (known as not conductor) does not need it with PBE, so I don't know why I should add smearing with PBE0.

I gave a try to HSE instead of PBE0. Same oscillations. There is something wrong with vc-relax and hybrid xc functionals.

[cid:61a1742b-37e7-41bb-81af-c20dd2d531a6]
Best,
Xavier
________________________________
From: Bidault, Xavier <xavbdlt at uic.edu>
Sent: Tuesday, January 26, 2021 9:50 AM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] vc-relax with PBE0 not converging

Hello,

My system is an organic molecular crystal (atoms C, H, N, O). The cutoff is chosen so there is 2 meV/atom error for SCF energy. The k-point grid 3x2x3 (off-centered) yields perfectly converged SCF energy. But to get faster with the vc-relax, I lowered it to 2x1x2 (off-centered), which introduces an error of only -0.1 meV/atom. I don't know if this is the reason why vc-relax density and pressure oscillate without converging.

I'm currently running v-relax with 3x2x3 grid... waiting for the result (10x slower)...

Thank you,
Xavier
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Paolo Giannozzi <p.giannozzi at gmail.com>
Sent: Monday, January 25, 2021 9:38 AM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] vc-relax with PBE0 not converging

Maybe the same problem reported here?
   https://gitlab.com/QEF/q-e/-/issues/204<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.com%2FQEF%2Fq-e%2F-%2Fissues%2F204&data=04%7C01%7Cxavbdlt%40uic.edu%7C3fdf0cc0f8bd4cd43e8308d8c14769ce%7Ce202cd477a564baa99e3e3b71a7c77dd%7C0%7C0%7C637471859758045446%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=QCUVoTzncfJfau7FM88IUZSHHmCHJf9wUl50miJJ4W4%3D&reserved=0>
Paolo

On Mon, Jan 25, 2021 at 4:19 PM Bidault, Xavier <xavbdlt at uic.edu<mailto:xavbdlt at uic.edu>> wrote:
Hello,

I have a molecular crystal (1 unit cell = 56 atoms). I use SG15 ONCV 1.2 pseudopotential and Grimme D2 correction.
Using vc-relax with PBE, the structure converges, no problem.
But with PBE0, density and pressure oscillate without dampening (see figure below - Pressure remains negative, and not close to zero). Is there any particular strategy with PBE0?

  *   vc-relax with PBE and then starting from the result and use PBE0?
  *   relax with PBE0 and then vc-relax?
  *   any simulation parameter to change (ion dynamics and/or cell dynamics - currently BFGS)?
  *   any strategy with PBE0?

[cid:1773a31d564cb971f161]
Thank you,
Xavier

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Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

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