[Pw_forum] difference in energy calculated by "gaussian" and "m-v" smearing

[mohnish pandey]

Thank you so much Dr. Marzari and Lorenzo....

On Wed, Nov 25, 2009 at 6:01 PM, Nicola Marzari <marzari at mit.edu> wrote:

>
> Dear Mohnish,
>
> roughly speaking you should use a similar degauss for m-v and gaussian.
> .05 Ry is fairly large, I'd stick with
> .02 Ry or so.
>
> Try this - study a bulk system (i.e. as small as possible) and plot for
> 3 or 4 k-point meshes the free energy (E-TS)
> as a function of smearing. At very small smearings the free energy will
> not be converged with respect to k-points;
> at high smearings it will, but will also be very dependent on smearing.
>
> You want the sweet spot in between.
>
>                   nicola
>
>
> mohnish pandey wrote:
> > Dear users,
> >                       I have calculated the energy of zinc oxide thin
> > film having nine layers. But the energy calculated by "m-v" and
> > "gaussian" smearing is coming out to be very different. The difference
> > is around 0.1 Rydberg. I have used used "degauss" to be .05 and 10^-3
> > respectively for "m-v" and "gaussain smearing". Can anybody please
> > tell me why the energy is coming out to be very different. I have gone
> > through the sections of book by Martin and Sholl also but I couldnt
> > find that.
> >
> > Sincere thanks in advance.
> > Mohnish Pandey
> >
> >
> > --
> > Mohnish Pandey
> > Y6262,4th Year Undergraduate,
> > Department of Chemical Engineering,
> > IIT KANPUR
> > ------------------------------------------------------------------------
> >
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>
>
> --
> ---------------------------------------------------------------------
> Prof Nicola Marzari   Department of Materials Science and Engineering
> 13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
> tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
>
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-- 
Mohnish Pandey
Y6262,4th Year Undergraduate,
Department of Chemical Engineering,
IIT KANPUR
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