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

Dear Fabien,

Thank you for another important suggestion on the GW calculation. I very much appriciate that.

Kind regards,

Thanusit


On April 24, 2008 2:39:59 PM ICT, "Fabien Bruneval" <fabien.bruneval@cea.fr> wrote:

Dear Thanusit,

Let's say that if you perform your convergence tests and also your
production runs with the complete k-point grid, you are on the safe side.
Maybe you can do some convergence tests with a reduced k-point grid, but
when turning to production, you should not forget to have a complete grid.

My main worry was that most of the beginners, which train with the
tutorial using only 1 k-point, think that only one k-point is needed in
general.
I have the feeling that it is not clear from the tutorial that the 1
k-point run is just meant for testing purposes, and that for all
real-life GW, one absolutely needs the complete Monkhorst-Pack grid...
That's why I was proposing to change the tutorial.

Best regards.

Fabien


ธนูสิทธิ์ บุรินทร์ประโคน wrote:
>
> Dear Fabien,
>
> Acoording to your recent sugestion on the k-point grid needed in GW
> calculations, does it mean that the KSS file must be generated by
> using a complete k-point grid in the first place before we perform the
> convergence tests and all sucessive calculations?
>
> Kind Regards,
>
> Thanusit
>
>
> */On April 22, 2008 4:01:54 PM ICT, "Fabien Bruneval"
> wrote:/*
>
> Dear Sophie,
>
> This tutorial is rather misleading and should be changed in the
> future.
>
> The GW calculations needs a k-point grid similar to the one uses
> in the
> usual DFT calculations.
> The only requirement is that the k-point, where you want to know
> the GW
> band structure, needs to be part of the k-point grid you use.
>
> A shortcoming of the current state of the GW part is that it is not
> really clever in using the symmetries. Therefore, it is generally
> a good
> policy to
> choose a k-point grid that is centered in Gamma or with the usual
> shift
> 0.5 0.5 0.5. Other choices usually perturb the code, which
> produces tons
> of k-points
> in the Brillouin Zone.
>
> If you want to calculate the GW correction in a weird k-point,
> such as
> [0.3 0.3 0.], I advise to you to calculate the GW corrections in a
> "nice" neighboring point like [0.25 0.25 0], which is part of you
> k-point grid. And then use this GW correction on top of DFT
> calculation
> made in the precise k-point you wanted.
>
> e_GW(k=0.3) = e_KS(k=0.3) + [ e_GW(k=0.25) - e_KS(k=0.25) ]
>
> This is justified because usually the term within squared brackets is
> rather k-point insensitive.
>
> I'm not sure to be clear enough... If not, just tell me.
>
> Fabien
>
>
> us_sophie.green@yahoo.com wrote:
> > Dear all users,
> >
> > I looked the tests in abinit about the GW calculations. In the
> GW corrections
> > for the band gap, the convergence tests (including ecutwfn,
> ecutsigx, nband,
> > etc) have done within only one point (the gamma point for Si). I
> am not sure of
> > its accuracy. Besides, the band gap correction for Si is in
> gamma point (direct
> > band gap semiconductor), whether the convergence test on gamma
> point is
> > revelant to the following calculation of the band gap correction
> in Gamma
> > point?
> > If I want to calculate the GW correction for the band gap with a
> nonspecial
> > point, for example (0.3 0.3 0), should I test the parameters
> with the (0.3 0.3
> > 0) point, other than gamma point? The point (0.3 0.3 0) should
> be included in
> > the KSS calculation, then I wrote my input file in the Dataset2
> part as
> > follows. I give three points including (0.3 0.3 0) ( the other
> two points are
> > interesting points, with which I will also do GW corrections). I
> am not sure
> > whether it is feasible.
> > Need your help. Thanks in advance.
> >
> >
> > # Dataset2: calculation of kss file
> > # Definition of k-points
> > kptopt2 0
> > nkpt2 3 # A set of 19 k-points containing Gamma
> > kpt 0.3 0.3 0
> > 0.5 0.5 0
> > -0.5 0.5 0
> > #istwfk2 19*1 # Option needed for Gamma
> > istwfk2 3*1
> > iscf2 -2 # Non self-consistent calculation
> > getden2 -1 # Read previous density file
> > nband2 13
> > nbandkss2 -1 # Number of bands to store in KSS file
> >
>
>
>