[QE-users] SCF convergence issue after first ionic step
Laurent Pizzagalli
laurent.pizzagalli at univ-poitiers.fr
Tue Dec 19 11:08:10 CET 2023
Hi Giovanni,
thank you for your help.
Actually I already tried to start the calculations with different
smearing values, or different mixing schemes. I also tried to add small
perturbations to the ionic positions, because I initially thought that I
was caught in the a "weird" state. But with no improvements.
I do not understand the issue, because if I start the calculations with
the atomic positions obtained after the first ionic relaxation step, the
scf calculation ran fine. It seems to me that if
'pot_extrapolation=none' and 'wfc_extrpolation =none', the scf
calculation at the n+1 ionic relaxation step does not use information
from the electronic structure relaxed at ionic step n (i.e. it is
equivalent to running a scf calculation from scratch). Is somebody can
confirm this aspect (or explain to me how and why I am wrong?) ?
Best regards
Laurent
On 19/12/2023 10:29, Giovanni Cantele wrote:
> Hi, I do not have a precise explanation of that, but I can say that I
> found such a behavior several times, in the years,
> for completely different systems.
> And this concerns not only the convergence of the scf step, but also
> the relaxation
> of the atomic positions.
> At some iteration it seems that the algorithm falls in some "potential
> well" and cannot exit it at all.
>
> In this respect, it helps often just to restart the calculation from
> scratch using one of the last coordinate sets found by
> the pw.x, or in some cases restart the code introducing in the
> coordinates even very small perturbations (e.g. delete the
> digits from the fourth to the last). In other cases, you might try to
> increase the smearing, even just for a few steps, mostly if
> the problem is the convergence of the scf cycle.
> This is just empirical, but it is the signature for tricky
> calculations (where there is no parameter
> to identify when a calculation is going to become "tricky"!), where
> the presence of local minima or other numerically hard problems,
> either with respect to the charge density or with respect to the
> atomic positions, can make the convergence non as easy as expected.
>
> Maybe, someone more expert might add some more specific hints.
>
> Giovanni
>
> --
>
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it <mailto:giovanni.cantele at spin.cnr.it>
> Phone: +39 081 676910
> Skype contact: giocan74
>
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: https://sites.google.com/view/giovanni-cantele/home
>
>
> Il giorno mar 19 dic 2023 alle ore 08:49 Laurent Pizzagalli
> <laurent.pizzagalli at univ-poitiers.fr> ha scritto:
>
> Dear all,
>
> I came across an issue I never encountered before. I performed a
> simple
> ionic relaxation of a W cluster. The initial scf convergence is
> achieved, the ionic forces are calculated (and are reasonable for a
> first ionic relaxation step) and the new atomic positions are
> obtained.
> The issue arises during the next scf calculation, which diverges in a
> few steps. However, if I start a new calculation with the updated
> ionic
> positions as input structure, the scf calculation runs smoothly and
> converges (but the issue occurred again for the next ionic relaxation
> steps).
> I obtained the same behavior with two different pw.x versions (6.7
> and
> 7.1). I also tried to set 'pot_extrapolation = none', but with no
> difference...
>
> Do any of you have an idea about the origin (and solution) of this
> issue ?
>
> Thanks
>
> Laurent
>
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> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
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/'^'\ |__|
( o o ) |
--------------------------------------------------oOOO--(_)--OO|o------
<Laurent.Pizzagalli at univ-poitiers.fr>
http://laurent.pizzagalli.free.fr/ Tel +33 549 49 74 99
------------------------------------------ Fax +33 549 49 66 92
Institut P'
Departement de Physique et de Mécanique des Matériaux
CNRS UPR 3346
Université de Poitiers
SP2MI
TSA 41123 .oooO
86073 Poitiers Cedex 9, FRANCE ( ) Oooo.
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