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[Emmanuel Arras <emmanuel.arras@cea.fr>]

ok, I tried to improve k-mesh (16x16x16 => 288 kpts (kptrlen = 87) as compared to 8x8x8 => 40 kpts (kptrlen = 32) previously ) and increase nband (up to 32 bands (now 13 are empty for spin up, and 19 for spin down) as compared to 24 bands previously ( 5 and 11 empty) ). It gives the same result : convergence is very very slow with ecutsm, but not without !

Concerning the pseudopotential, I used the one given one the abinit download page (http://www.wfu.edu/~natalie/papers/pwpaw/periodictable/atoms/Fe/index.html). I guess Josef Zwanziger used the same.

I think the problem may indeed be connected to the parallelization. I still have to perform the calculations with abinis to see.

Another thing I mentioned earlier : if I remove the symmetries (nsym 1), the convergence is really difficult, but the calculation without ecutsm is still faster. (Fe-BCC_ecutsm_aniso_nsym_1.png attached).

And finally, a plot of convergence as a function of ecutsm (Fe-BCC_ecutsm_aniso.png attached). The dependence is obvious.

I'll keep you updated.
Thanks

Emmanuel ARRAS


matthieu verstraete a écrit :

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On Tue, Dec 16, 2008 at 12:08 PM, Emmanuel Arras <emmanuel.arras@cea.fr> wrote:

I'm not quite sure I understand what you are saying, so correct me if I'm wrong :
- You tried my input file, and found a very very slow convergence (the same as me).
 

- To see the difference with ecutsm, you tried to remove ecutsm from my input, and launched it. You also got a very very slow convergence (=> that's why you say there is no big difference with ecutsm). Then I don't understand why we get different results.

maybe the pseudopotential. I don't think you misran or miscompiled abinit, it's just a conjunction of factors (underconvergence of some, magnetism, etc) which allow this effect of ecutsm.

I tried to inprouve my calculations as you told, and as soon as these calculations with a denser kpt coverage and more bands are finished, I will let you know. Still, I just need to remove ecutsm to get a good convergence...

It may be something to do with the interplay between ecutsm and the parallelization. The block-parallel algorithm is trickier than the standard one where all the bands are kept together. This may be the source of differences in the SCF.

Joe - were you using the parallelization on bands?
 

Matthieu

--
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Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
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