[Pw_forum] dos

[Prasenjit Ghosh]

Hi Jonas,

For DOS calculations one needs to do an integration over the kpts in the
Brillouin zone. So you need a very fine k-point mesh than necessary for a
scf calculation. Moreover you need a large number of bands. Doing an scf
calculation with such a fine k-point mesh and so many bands is very
expensive. So you should first do an scf calculation with the min. no. of
k-points and bands and then do a nscf calculation with a finer k-point and
larger no. of bands. In the nscf step, the code does an interpolation for
the extra bands and k-points and not a self-consistent calculation. This
saves computational time.

Hope this helps.

Prasenjit.

2009/5/3 Jonas Baltrusaitis <jasius_1 at yahoo.com>

>
> Prasenjit,
>
> could you explain why both scf followed by nscf calculations are needed for
> DOS calculations, as per example 8? If only scf density is needed for
> further projection, why not to calculate only one?
>
> Jonas
>
>
> --- On Sun, 5/3/09, Prasenjit Ghosh <prasenjit.jnc at gmail.com> wrote:
>
> > From: Prasenjit Ghosh <prasenjit.jnc at gmail.com>
> > Subject: Re: [Pw_forum] dos
> > To: "PWSCF Forum" <pw_forum at pwscf.org>
> > Date: Sunday, May 3, 2009, 2:00 PM
> > dear all user
> > >
> >
> > Dear Yaldaa,
> >
> >
> > > How can I project dos to molecular orbital?
> > >
> >
> > There is a post-processing tool called projwfc.x which you
> > can use to
> > project dos to molecular orbital.
> >
> > what is the importance of nbnd in calculations for dos?
> > >
> > e
> > "nbnd"  tells the code the no. of Kohn-Sham
> > states it has to
> > compute.....While computing the dos, one wants to plot the
> > dos for both the
> > occupied & unoccupied manifold, the no. of energy
> > levels is read in by the
> > dos.x from the output of your scf/nscf run. So while doing
> > an scf/ nscf
> > calculations you can control the total no. of states with
> > the variable
> > "nbnd".
> > Depending on the type of occupation scheme you choose the
> > value of nbnd is
> > nelec/2 (fixed occupation)  or nelec/2+some extra bands
> > (when you use
> > smearing). If you want to plot the dos, usually you should
> > add some extra
> > levels using nbnd & do the scf or nscf calculations to
> > get the unoccupied
> > manifold.
> >
> > and for plottingdos or pdos, if the fermi energy is assumed
> > to be zero
> > > automatically by program?
> > >
> >
> > No, you have to do the alignment yourself
> >
> > With regards,
> >
> > Prasenjit.
> >
> >
> >
> > --
> > PRASENJIT GHOSH,
> > POST-DOC,
> > ROOM NO: 265, MAIN BUILDING,
> > CM SECTION, ICTP,
> > STRADA COSTERIA 11,
> > TRIESTE, 34104,
> > ITALY
> > PHONE: +39 040 2240 369 (O)
> >              +39 3807528672 (M)
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
>
>
>
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-- 
PRASENJIT GHOSH,
POST-DOC,
ROOM NO: 265, MAIN BUILDING,
CM SECTION, ICTP,
STRADA COSTERIA 11,
TRIESTE, 34104,
ITALY
PHONE: +39 040 2240 369 (O)
             +39 3807528672 (M)
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