[Pw_forum] RE : RE : A question on atomic magnetic moments

[saqib.javaid at ipcms.u-strasbg.fr]

Dear Nicola,
with regards to your comments "it keeps you company during the voyage,
> but shouldn't share your bed...", does this mean that smearing contribution
print as "-TS" should be less than convergence criteria (typically 1mry) with
regards to increase in no. of K points and KE cut-off for a SCF calculation?
I would appreciate a clarification
with best regards
saqib javaid
University of strasbourg.

Selon Nicola Marzari <nicola.marzari at materials.ox.ac.uk>:

>
>
> Dear Giovanni, Cyrille,
>
>
> the iron dimer has a very complex electronic structure (see e.g. our
> PRL 2006 Kulik et al) - different multiplets, and for each multiplet,
> different symmetries.
>
> In principle, there is no way to guess to which of the many
> self-consistent states you'll converge to, and I suppose that what
> you have here is that you have converged to different states.
> You'll need to look at the total energy, kohn-sham eigenstates, and the
> symmetry of those to understand what you are looking at
> (also, there is no point in having more bands than efermi + 3*degauss -
> empty bands above that threshold are useless).
>
> There is no easy way to force the code into one state or the other -
> you could try using GGA+U - some U's will stabilize reliably one state,
> and then by reducing smoothly the U (or increasing it) you might be able
> to have (as a function of U) the energy of your preferred electronic
> configuration.
>
> Last - for a cluster or a molecule smearing is used, somewhat
> inappropriately, to help a calculation converge when using
> iterative approaches - it keeps you company during the voyage,
> but shouldn't share your bed (the real reason d'etre for
> smearing is to improve k-point integrations in metals).
>
> 				nicola
>
>
> On 2/15/11 5:42 PM, Giovani Faccin wrote:
> > Dear Cyrille,
> >
> > I recalculated the dimer with different values of nbnd. Now some
> > interesting changes appeared:
> >
> > Value of nbnd    |   Magnetization
> >
> > 10     4.00
> > 12     6.88
> > 14     6.49
> > 16     6.49
> > 18     6.49
> > 20     6.49
> > 22     6.88
> > 24     6.88
> > 26     6.49
> > 28     6.49
> >
>
>
> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari    Department of Materials    University of Oxford
> Chair of Materials Modelling  Director, Materials Modelling Laboratory
> nicola.marzari at materials.ox.ac.uk     http://mml.materials.ox.ac.uk/NM
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