[Pw_forum] Fermi energy in 'scf' and 'nscf'(XQ Wang)

[Stefano de Gironcoli]

Dear Haiping,
the ONLY Fermi energy that is meaningful is the one corresponding to a 
scf calculation... which is calculated  consistently with the 
corresponding  charge density.
All nscf or band calculations are performed  on grids which might  give 
non-regular sampling of the BZ...  you should not use the corresponding 
fermi energy .
stefano

lan haiping wrote:
> dear hande,
> i do wonder a point about fermi energy.
> when we draw a bands along high symmetry points, which
> values of fermi energy we should do align with ?  the situation of 
> 'nscf' calculation with large BZ sampling ,or just
> the 'bands' calculation along the high symmetry points ?
> Bests,
>
> On Wed, Aug 13, 2008 at 8:22 PM, Hande Ustunel 
> <hande at newton.physics.metu.edu.tr 
> <mailto:hande at newton.physics.metu.edu.tr>> wrote:
>
>     Dear Prasenjit,
>
>     > If the difference in Fermi energy is quite large, what I would
>     suggest is to
>     > increase the no. of k-points in the nscf cal. & redo it.
>
>     The fact that Guoying's nscf calculation was conducted along high
>     symmetry
>     points suggests that it was to be followed by a band structure
>     run. In that
>     case, it is not necessary to try to obtain a "good" Fermi energy
>     from the
>     nscf run other than convince oneself since this is not the point
>     here. Besides, I don't think increasing the number of kpoints
>     along these
>     high symmetry directions would mean much because since you would
>     still have
>     a severely heterogeneous sampling. It should just sufficient to
>     just draw
>     the band structure from nscf along with the Fermi energy from the scf
>     calculation. But you would be absolutely right if what we were
>     trying to do
>     here was to, say, increase resolution in a DOS plot.
>
>     On a separate note, I suggest that you try bands rather than nscf
>     if you
>     are trying to draw a band structure since nscf worries about
>     symmetries and
>     creates extra points whereas bands just does the ones you ask it
>     to do.
>
>     Best,
>     Hande
>
>     --
>     Hande Toffoli
>     Department of Physics
>     Office 439
>     Middle East Technical University
>     Ankara 06531, Turkey
>     Tel : +90 312 210 3264
>     http://www.physics.metu.edu.tr/~hande
>     <http://www.physics.metu.edu.tr/%7Ehande>
>
>
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>
>
> -- 
> Hai-Ping Lan
> Department of Electronics ,
> Peking University , Bejing, 100871
> lanhaiping at gmail.com <mailto:lanhaiping at gmail.com>, hplan at pku.edu.cn 
> <mailto:hplan at pku.edu.cn>
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