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[ธนูสิทธิ์ บุรินทร์ประโคน <thanusit@kku.ac.th>]

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Dear Matteo Giantomassi

Thank you very much for your very kind and helpful suggestion.

Best Regards,
Thanusit Burinprakhon

> On December 4, 2007 12:33:32 AM ICT, "Matteo Giantomassi"
<gmatteo@pcpm.ucl.ac.be> wrote:
> 
> 
> On Sun, 2 Dec 2007, thanusit@kku.ac.th wrote:
> 
> > Dear all Abinit members
> >
> > I'm trying to prepare the KSS file for GW calculation of Si-band,
with the parallelized abinit version 5.4.3. The input for KSS generation
is as below:
> >
> > --------------------------
> > # Dataset2: calculation of kss file
> > nkpt2    19
> > nshiftk2  4
> > shiftk2  0.0 0.0 0.0
> >         0.0 0.5 0.5
> >         0.5 0.0 0.5
> >         0.5 0.5 0.0
> > istwfk2  19*1
> > iscf2    -2
> > getden2  -1
> > nband2   10
> > nbandkss2 100
> > kssform2  3
> > tolwfr2  1.0d-10
> > --------------------------------
> >
> > The calculation was completed. I found that the number of bands
stored in the kss file was 10 instead of 100 as specified by nbandkss2.
The part of the output looks like this:
> >
> > ======================================================================
> > Calculating and writing out Kohn-Sham electronic Structure file
> > Using conjugate gradient wavefunctions and energies (kssform=3)
> > number of Gamma centered plane waves    507
> > number of Gamma centered shells     41
> > number of bands     10
> > maximum angular momentum components      3
> > Conjugate gradient eigenvalues
> >   k    eigenvalues [Hartree]
> >   1     -0.2183  0.1626  0.1824  0.1824  0.2841  0.3474  0.3474
 0.3664  0.4523
> >          0.5137
> > ......
> >
> > However, as I set the kssform2  to 1, the number of bands stored in
the kss file was 100 as expected. My points are:
> >
> > 1. Is this the usual result when we set the kssform = 3?
>    Yes. When kssform is 3, the code uses the conjugate gradient to
converge the states
>    specified by nband, not nbandkss. When the wavefunctions are
converged below tolwfr,
>    the SCF cycle exits and  nbandkss states are written on the KSS file.
> 
>    In your case you are asking for 100 states for the KSS, but only 10
bands are available.
>    Abinit is smart but it's not yet able to create converged
wavefunctions from nothing,
>    we are still working on it :)
> 
>    To obtain 100 bands in the KSS file you should use nband2=100 and
 nbandkss2=100.
>    Moreover it's worth to add a buffer during the SCF run; you might try:
> 
>    nband2=105
>    nbandkss2=100
>    nbdbuf 5       #see
http://www.abinit.org/Infos_v5.5/input_variables/vargs.html#nbdbuf
> 
> 
> > 2. In the convergence study of GW corrections with respected to
nband, we need to vary the nband to some value beyond 10. Suppose the
number of bands stored in the KSS file is 10, can we still do so (set
nband above 10) without getting incorrect results?
> 
>     If the number of bands found in the KSS file is less than the number
>     of states specified by nband, the code prints a WARNING and
proceeds with the available states.
>     In your case the results are not wrong, only not converged and
completely unreliable as few bands are employed.
> 
>    Hope this helps,
>    Best Regards
>    Matteo Giantomassi
> 
> > Besr regards,
> > Thanusit Burinprakhon
> >
> >