[Pw_forum] occupations fixed

[udayagiri sai babu]

Dear Lorenzo thanks for the answer. My problem is simple it is to find out
the cohesive energy of Cr,V,Ti. I posted this question earlier also. I was
told to try out with occupations=from_input instead of degauss value to get
the accurate value of the ground state energy because i am getting an error
of around 10% in Ec (i was wondering if that can be acceptable) meanwhile i
came across the post which says to use ocuupations=fixed.

On Wed, Oct 7, 2009 at 1:09 PM, Lorenzo Paulatto <paulatto at sissa.it> wrote:

> In data 07 ottobre 2009 alle ore 09:24:28, udayagiri sai babu
> <udayagiri3 at gmail.com> ha scritto:
>
> > In the archive I have seen a discussion suggesting use of
> > occupations=fixed to find out the ground state energy of isolated oxygen
> > atom accurately. Can I use the same (occupations=fixed) for metal also.
> > Because in the pw
> > document it is told to use only for insulators.
>
>
> Dear U,
> for isolated atoms you can always use fixed occupations: as you use only
> use the Gamma point, bands are actually flat. Nevertheless it may be
> difficult to reach the ground state in some cases, I suggest using a small
> smearing which should give exactly the same result but makes convergence
> faster.
>
> I see you have already asked how to compute the ground state for a Ti atom
> (e.g.
> <http://www.democritos.it/pipermail/pw_forum/2009-September/014246.html>),
> which actually is a metal... why don't you tell us your problem, instead
> of your guess for a solution?
>
> best regards
>
> --
> Lorenzo Paulatto
> SISSA  &  DEMOCRITOS (Trieste)
> phone: +39 040 3787 511
> skype: paulatz
> www:   http://people.sissa.it/~paulatto/<http://people.sissa.it/%7Epaulatto/>
>
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-- 
U.Saibabu
PhD student,
Deformation mechanisms modeling group,
Materials engineering department,
IISc Bangalore,
India.
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