[Pw_forum] RE : A question on atomic magnetic moments

Nicola Marzari nicola.marzari at materials.ox.ac.uk
Tue Feb 15 12:29:46 CET 2011

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).


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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