[gpaw-users] Wavefunction convergence problem
Ask Hjorth Larsen
asklarsen at gmail.com
Wed Jul 16 15:17:26 CEST 2014
Hello Gaël
How about (always :)) sending the log file to check whether anything
else might be acting up? This does not normally happen in exactly
that way. I think.
Best regards
Ask
2014-07-16 15:09 GMT+02:00 Gaël Donval <gael.donval at cnrs-imn.fr>:
> Increasing the amount of vacuum did the trick: my structure is now
> relaxed. I thought vacuum was needed only to achieve total energy
> convergence, it appears that it also helps for the SCF convergence.
>
> I'm surprised that such a large vacuum is needed. I reduced the vacuum
> to 7A and observed a similar error oscillation after a few atomic
> relaxation cycles which corresponded to the expansion of the slab along
> the non periodic direction which induced a reduction of the total vacuum
> space.
>
> At least the error oscillation is easy to spot.
>
> Thanks for your suggestions Ask.
>
> Gaël
>
> Le mercredi 16 juillet 2014 à 12:45 +0200, Gaël Donval a écrit :
>> Nope, didn't work. The error is still oscillating. To GPAW's defense,
>> the system is really tricky and VASP took a *lot* of iterations to reach
>> convergence.
>>
>> I also tried to decrease the grid spacing to 0.12. It's very low, I
>> know, but at least I'm sure this won't be a problem.
>>
>> I think I may have found the culprit. I had put 5 A of vacuum in the
>> non-periodic direction. By raising this amount to 10 A, I could make the
>> wavefunction converge. That's a shame that empty space is not free :)
>>
>> Gaël
>>
>> Le mercredi 16 juillet 2014 à 11:56 +0200, Ask Hjorth Larsen a écrit :
>> > Okay. I would recommend another k point in the short direction then.
>> > El 16/07/2014 11:55, "Gaël Donval" <gael.donval at cnrs-imn.fr> escribió:
>> >
>> > > Hi Ask,
>> > >
>> > > The smearing temperature is 0.1 eV.
>> > >
>> > > Regards,
>> > > Gaël
>> > >
>> > > Le mercredi 16 juillet 2014 à 11:46 +0200, Ask Hjorth Larsen a écrit :
>> > > > Hi Gaël
>> > > >
>> > > > What is the smearing temperature?
>> > > >
>> > > > Best regards
>> > > > Ask
>> > > > El 16/07/2014 10:37, "Gaël Donval" <gael.donval at cnrs-imn.fr> escribió:
>> > > >
>> > > > > Hi,
>> > > > >
>> > > > > I have generated a quite a big slab (80 atoms, time reversal symmetry
>> > > > > only) with ASE and try to perform structure optimization on it.
>> > > > >
>> > > > > Unit Cell:
>> > > > > Periodic X Y Z Points
>> > > > > Spacing
>> > > > >
>> > > > > --------------------------------------------------------------------
>> > > > > 1. axis: no 23.278154 0.000000 0.000000 128
>> > > > > 0.1819
>> > > > > 2. axis: yes 0.000000 7.679180 0.000000 40
>> > > > > 0.1920
>> > > > > 3. axis: yes 0.000000 0.000000 8.145000 48
>> > > > > 0.1697
>> > > > >
>> > > > >
>> > > > > I use only one k-point (gamma).
>> > > > >
>> > > > > When I first tried to get SCF convergence, I couldn't even converge to
>> > > > > anything, even with very low mixing parameters. I had to remove bands
>> > > > > (from nelectron to 25 unoccupied bands) to get the convergence that you
>> > > > > will see bellow.
>> > > > >
>> > > > > At the first relaxation step, in the SCF calculation, everything
>> > > > > converges smoothly down to some point then hits a limit: the error on
>> > > > > the density stays around 10^-4 and the error on the wavefunction is
>> > > > > switching between two values. For instance:
>> > > > >
>> > > > > iter: 47 10:02:07 -3.19 -4.20 -356.939274 2 2
>> > > > > iter: 48 10:02:09 -3.11 -4.13 -356.938830 2 3
>> > > > > iter: 49 10:02:12 -3.19 -4.43 -356.938031 2 2
>> > > > > iter: 50 10:02:14 -3.11 -4.49 -356.937563 2 2
>> > > > > iter: 51 10:02:17 -3.19 -4.60 -356.937381 1 1
>> > > > > iter: 52 10:02:20 -3.11 -4.57 -356.937543 1 1
>> > > > > iter: 53 10:02:22 -3.19 -4.59 -356.938149 1 1
>> > > > > iter: 54 10:02:25 -3.11 -4.56 -356.937988 1 1
>> > > > > iter: 55 10:02:27 -3.19 -4.53 -356.938700 2 2
>> > > > > ...
>> > > > > iter: 283 10:12:19 -3.15 -3.84 -356.893178 2 2
>> > > > > iter: 284 10:12:22 -3.08 -4.34 -356.882750 1 1
>> > > > > iter: 285 10:12:24 -3.15 -4.55 -356.858456 2 2
>> > > > > iter: 286 10:12:27 -3.08 -4.24 -356.864220 2 1
>> > > > >
>> > > > >
>> > > > > If I consider that this is enough and stop there, then I got the same
>> > > > > behavior in the second step with the error on the density converging to
>> > > > > ~10^-4 *but* the error on the wavefunctions stays at ~10^-1.4 (same
>> > > > > behavior, switches between two values).
>> > > > >
>> > > > > I followed the recommandations on the "Convergence issues" web page,
>> > > > > without success. I also tried different mixers and eigensolvers.
>> > > > >
>> > > > > Does anyone has an idea about that?
>> > > > >
>> > > > >
>> > > > > _______________________________________________
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>> > > > > gpaw-users at listserv.fysik.dtu.dk
>> > > > > https://listserv.fysik.dtu.dk/mailman/listinfo/gpaw-users
>> > > > >
>> > >
>> > >
>> > >
>>
>>
>>
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