[gpaw-users] Wavefunction convergence problem

Wed Jul 16 15:09:36 CEST 2014

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?
> > > > >
> > > > >
> > > > > _______________________________________________
> > > > > gpaw-users mailing list
> > > > > gpaw-users at listserv.fysik.dtu.dk
> > > > > https://listserv.fysik.dtu.dk/mailman/listinfo/gpaw-users
> > > > >
> > >
> > >
> > >
> 
> 
> 
> _______________________________________________
> gpaw-users mailing list
> gpaw-users at listserv.fysik.dtu.dk
> https://listserv.fysik.dtu.dk/mailman/listinfo/gpaw-users
> 

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 4053 bytes
Desc: not available
URL: <http://listserv.fysik.dtu.dk/pipermail/gpaw-users/attachments/20140716/5ab3a055/attachment-0001.bin>