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[Zeila Zanolli <zeila.zanolli@uclouvain.be>]

Yes, in my experiece it is exactly like that:  position of the kpoints in the reciprocal lattice + symmetries.

Indeed, a similar situation happens with the SIESTA code, where the symmetries are not 'recognized' as in ABINIT.

The convergence of whatever "something" will oscillate with the k-mesh and to get it right one has to go to really high value of k-mesh.

The convergence of the scf cicle is more difficoult for k-meshes not including the 1/3 1/3.....

To achieve the convergence of the scf cicle I'm using a very tiny mixing factor in the pulay mixing scheme.

Zeila

On 5 Mar 2009, at 00:37, matthieu verstraete wrote:

Hmmm, this is very interesting! It looks like it depends on the kpoint sampling including the K point or not (1/3 1/3 in recip space)... This is of course the only point on the Fermi surface. However the residuals are not only bad at K... So it's the combination of having the K point and not having the appropriate symmetrizations, but I don't know how this plays in to the conditionning of the convergence.

Matthieu

On Wed, Mar 4, 2009 at 6:08 PM, Anglade Pierre-Matthieu <anglade@gmail.com> wrote:

Hi Matthieu,

Have you noticed that there is two case depending on your k-point mesh ?
In the wrong case, obtained with meshes like 36 36 1, 12 12 1, 9 9 1,
6 6 1, the potential residual you get is a function of the number of
k-point you use :The less k-point,  the bigger the vres2.
Yet If one uses a single k-point or some other meshes (tried 211, 221,
441, 551, 771, 881, 35 35 1)  everythings converge fine.

If one or a few k-point were getting a  "shift"  because of bad
application of symmetries in the nonsymmop case,  don't you think it
could lead to this behavior ?

Have you already explored this idea ?

Regards

PMA

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Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
Dpto. Fisica de Materiales, 
U. del Pais Vasco,            
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390

Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500

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Dr. Zeila Zanolli

Université Catholique de Louvain (UCL)

Unité Physico-Chimie et de Physique des Matériaux (PCPM) 

Place Croix du Sud, 1 (Boltzmann)

B-1348 Louvain-la-Neuve, Belgium

Phone: +32 (0)10 47 3501 

Mobile: +32 (0)487 556699

Fax: +32 (0)10 47 3452

e-mail: zeila.zanolli@uclouvain.be

web: http://www.nano2hybrids.net/

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