[Pw_forum] RE : A question on atomic magnetic moments

Giovani Faccin faccin.giovani at gmail.com
Tue Feb 15 17:15:37 CET 2011

```Dear Prasenjit and Nicola,

Thank you for the comment on smearing. I was not paying attention to it. A
quick look on some logs I have here show that this contribution is not that
much negligible in some calculations (around 0.00364895 Ry, for example).
Thus I'll evaluate the total energy as "!  total energy  - smearing
contribution(-TS)" from now on and see what I get.

I'm finishing a test battery based on another suggestion from the forum.
Once I report it, I'll take the best result from there and experiment with
smearing to see what we get from it.

Thanks again!

Giovani

2011/2/15 Nicola Marzari <nicola.marzari at materials.ox.ac.uk>

>
>
> Thanks Prasenjit - a further comment, to be careful about.
>
> In molecules/clusters, you could end up with a situation where
> the HOMO is degenerate, and you have fractional occupations,
> so the entropy term S is constant, and -TS is linear (T is deguass);
> this supposing the other states below the homo are separated
> from the HOMO by at least 2 or 3 times degauss.
>
> What you want is the total energy - that is obtained by
> subtracting the term "-TS" to the "total energy" printed
> by the code (since the "total energy" printed by the code,
> when you use a smearing, is not the total energy, but the
> total free energy E-TS).
>
>                                nicola
>
>
>
> On 2/14/11 5:22 AM, Prasenjit Ghosh wrote:
> > A small suggestion, try changing the smearing type, instead of using
> > mp, try using m-v or even simple gaussian is fine for small clusters.
> > Also, you should check the value of the contribution to total energy
> > from smearing (printed in the output after your calculations have
> > converged).......ideally for small clusters as yours, this should be
> > zero. This tells you that your smearing is physically small enough so
> > that the spurious effect of broadening becomes negligible.
> >
> > With regards,
> >
> > Prasenjit
> >
>
>
> --
> ----------------------------------------------------------------------
> 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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--
Giovani
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