[QE-users] scf of organic molecule does not converge

[Haoran Wang]

Thank you all for your answers and explanation. Adding smearing does make
things work now.

Thanks,
Haoran

On Wed, Jun 23, 2021 at 12:45 PM Stefano Baroni <baroni at sissa.it> wrote:

> Smearing may alleviate convergence problems in any case where the latter
> are due to level crossing during the SCF cycle. Absolute energy errors are
> not necessarily a good metric of the accuracy of a pseudopotential
> calculation, as they depend sensitively on the details of the (pseudo)
> wave-function in the atomic core, which hardly affect the measurable
> chemico-physical properties of your system (such as e.g. forces and energy
> differences in general). SB
>
> ___
> Stefano Baroni, Trieste -- http://stefano.baroni.me
>
> On 23 Jun 2021, at 17:26, Bidault, Xavier <xavbdlt at uic.edu> wrote:
>
> 
> I would say that an energy cutoff of 25 Ry is way too small. I also work
> on organic molecules, and I use 90 Ry (and 900 Ry for ecutrho) with PSlib
> 1.0.0 US to get errors lower than 1 meV/atom.
>
> @Paolo: I wonder how relevant it is to use smearing in an organic compound
> (unless it has conducting or semi-conducting capabilities). Could you tell
> why it would be something to do?
>
> Xavier B.
> ------------------------------
> *From:* users <users-bounces at lists.quantum-espresso.org> on behalf of
> Paolo Giannozzi <p.giannozzi at gmail.com>
> *Sent:* Wednesday, June 23, 2021 2:04 AM
> *To:* Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
> *Subject:* Re: [QE-users] scf of organic molecule does not converge
>
> It works decently well if you add a smearing (and a few more bands, but
> this is done automatically):
>    occupations      = 'smearing'
>    smearing         = 'gaussian'
>    degauss          = 0.01
>
> Paolo
>
> On Wed, Jun 23, 2021 at 8:12 AM Haoran Wang <whr1130 at gmail.com> wrote:
>
> Hi QE users,
>
> I have been trying to run the scf of a molecule below for many days. It
> never converged. The configuration is from Gaussian optimization, so it
> should be sensible. I did try other configurations obtained from MD
> simulations and still no convergence. I tried different pseudo-potentials
> (PBE-PAW, PBE-US, LDA-US) and also tried tuning the parameters
> (mixing_beta, mixing_mode, ecutrho...), still no convergence. Could
> somebody help me and see why this happens?
>
> Thanks,
> Haoran Wang
> Utah State University
>
>
> **************************************************************************************
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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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