The ABINIT Users Mailing List ( CLOSED )

["Fernando D. Vila" <fer@tiziano.phys.washington.edu>]

Dear Matthieu;

  Thank you very much for the answer. It makes complete sense. I have 
re-read the RF tutorial and it is cleanr to me now that I have to choose 
sets of kpoints and qpoints in the appropriate way.It takes time, but I'm 
learning.. :-)

  My impression is that this could be a common mistake. May I suggest that 
an extra line be added to the error messages suggesting that the user 
check the relation between those two sets?

Best regards and thanks again, Fer.

On Thu, 17 Nov 2005, Matthieu Verstraete wrote:

> Hello Fer,
>
> for each qpoint you need an explicit WFQ file containing the k+q eigenstates 
> and eigenvalues. With your 4x4x4 grid, the qpoint was a differnce of 2 
> kpoints, so you could use the original GS file as a WFQ file: ABINIT tries to 
> do the juggling of the kpoints from the GS file if no getwfq is specified.
>
> With 6x6x6, 1/4 0 0 is no longer a difference of 2 kpoints in the GS grid. 
> You must do the non scf calculation at k+(1/4 0 0) explicitly, as you do for 
> DS2 (where it is actually useless since q=0,0,0 is always a difference of two 
> kpoints). Actually, Umesh Wagmare told us at the abinit school this summer 
> that it is not very good practice at all to use qpoints not contained in the 
> kpoint mesh, and that systematic errors can be introduced.
>
> At a guess, I would say you'll need a lot more kpoints than 6x6x6 to 
> converge, so you might as well use a multiple of 4 (to contain all the 
> qpoints you use) and increase it further to 8x8x8, and probably even 12x12x12 
> or 16x16x16.
>
> Matthieu
>
> --
> ================================================================
> Dr. Matthieu Verstraete                 mailto:mjv500@york.ac.uk
> Dept. of Physics, University of York,     tel: +44 1904 43 22 08
> Heslington, YO10 5DD York, United Kingdom fax: +44 1904 43 22 14


Ubi dubium ibi libertas.
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Fernando D. Vila                Voice    (206)543-9697
Department of Physics           Fax      (206)685-0635
University of Washington        E-mail   fdv@u.washington.edu
Seattle, WA 98195, USA          WWW      http://faculty.washington.edu/fdv
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