The ABINIT Users Mailing List ( CLOSED )

[BOTTIN Francois <francois.bottin@cea.fr>]

Dear Carl, Joe and Emmanuel,

The problem comes from LOBPCG. And especially from the preconditioning 
within this algorithm.
This one depends on the kinetic energy, so that's the reason why ecutsm 
reveals (and not causes) the problem.
This trouble of convergence is also present in a few other systems which 
have been studied in our lab, with or without ecutsm.
Up to now, we have circumvent this problem by tuning some input parameters.
Try to increase: nline and/or nband and/or npband. Your calculations 
should work fine. Keep me in touch.

I'm aware that these tricks are only patchs and that the problem is deeper.
I'm interested these days in the preconditioning of LOBPCG and have a track.
The first results on various systems, which show no or poor convergence, 
are very good (these ones include the iron bcc system of emmanuel).
This correction improves strongly (several order of magnitude) the 
residual of the wave functions.
Before giving it to the community, I have to check that this correction 
is safe.
I will try to commit  it for the abinit 5.7 realease.

Francois

greeff@lanl.gov a écrit :
> Sorry if this a repetition. I tried to post before, but I don't see that it
> showed up. I was having a problem with convergence of the parallel code, and
> saw this thread, so I did some tests of the ecutsm option. The result is that
> there is an interaction of ecutsm /= 0 and wfotpalg = 4 that causes the
> problem. The problem occurs with parallel over band/fft, parallel over k-pt,
> and serial runs.
>
> My test case is for bct Sn, using a homegrown PAW from the Holzwarth code. I 
> am
> using abinit version 5.6.4, except the serial tests use 5.4.4. The compiler is
> intel 10.0.023 with openmpi. I can provide full input files if desired.
>
> This table summarizes the results. The number of iterations given is what is
> required for convergence with toldfe  1.0d-6. The entries with >n never
> converged to this tolerance.
>
> parallel ecutsm wfoptalg iter
>
>  band      1.0      4     >30
>  band      0.0      4      6
>  k-pt      1.0      4     >30
>  k-pt      0.0      4      6
>  k-pt      1.0     10      6
>  k-pt      0.0     10      6
>  serial     1.0     10     7
>  serial      1.0      4    >12
>
> The last serial run needed me to set fftalg 401, which wasn't used in the 
> other
> serial run. (It was used in all the parallel runs).
>
> Carl Greeff
>   


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Francois Bottin                    tel: 01 69 26 41 73
CEA/DIF                            fax: 01 69 26 70 77
BP 12 Bruyeres-le-Chatel         email: Francois.Bottin@cea.fr
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