[QE-users] SCF convergence issue after first ionic step
Paolo Giannozzi
paolo.giannozzi at uniud.it
Tue Dec 19 13:55:50 CET 2023
On 12/19/23 11:08, Laurent Pizzagalli wrote:
> It seems to me that with '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).
it is not exactly the same calculation, because
- if I remember correctly, the starting wavefunctions and charge
densities are anyway taken from the previous step
- thresholds on scf ans iterative diagonalization are computed differently
Hard to say why these rather minor differences lead to a different outcome.
Paolo
>
> 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
>>
>> --
>> ,,, __,
>> /'^'\ |__|
>> ( o o ) |
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>> <Laurent.Pizzagalli at univ-poitiers.fr>
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>> ------------------------------------------ Fax +33 549 49 66 92
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>> _______________________________________________
>> The Quantum ESPRESSO community stands by the Ukrainian
>> 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)
>> users mailing listusers at lists.quantum-espresso.org
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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.
> ----------------------------------------------------\ (----( )-------
> \_) ) /
> (_/
>
>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> 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)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
--
Paolo Giannozzi, DMIF, Univ. Udine, Italy
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