[Wien] Fermi level

[Laurence Marks]

A small comment: the definition of fermi energy, fermi level and chemical
potential is a question of semantics and confusion, see for instance
http://physics.stackexchange.com/questions/30922/whats-the-difference-between-fermi-energy-and-fermi-level

Since this is primarily a physics forum, it is probably best to stay with
the Fermi energy as T=0K and Fermi level = chemical potential at T > 0K.

If you use TEMPS in case.in2(c) an approximation of the chemical potential
is printed out. For a metal or small-gap insulator (semiconductor) it is
quite good; for a large-gap insulator for numerical reasons it is not right.

On Thu, Oct 20, 2016 at 8:39 AM, Fecher, Gerhard <fecher at uni-mainz.de>
wrote:

> The definition of the FERMI ENERGY that I gave is correct for every
> material: The Fermi energy is the energy of the highest occupied state at
> Zero temperature.
> It does not depend wheter or not your material is a metal, an intrinsic
> semiconductor, an doped semiconductor, an insulator, or anything else.
>
> Indeed, for metals the Fermi energy corresponds to the chemical potential
> (the quantity  that enters the Fermi-Dirac distribution)  at Zero
> temperature.
> but the chemical potential of a metal will also depend on temperature
> (Note: the chemical potential, not the Fermi energy, depends on
> temperature.).
>
> The Zero used in the electronic structure plots (DOS, band structure,
> etc.) of Wien2k is the Fermi energy as defined above,
> therefore, it is correct to have the Zero at the top of the valence band.
>
> By the way, you never defined what you mean with "Fermi level" and why it
> must be in the middle of the band gap.
> If you define for whatever reason that "Fermi level" is "the energy in the
> middle of the band gap" then your question does not make sense.
> However, if you like to stay with youre middle of the gap definition, then
> you should give a mathematical and physical proof that this is something
> usefull for all shapes of the density of states of a semi-conductor.
>
> If you like to know where the chemical potential in a certain
> semi-conducting material is then you may check with Boltztrap,
> you have to do the same that I did when its still not implemented there ,
> change the code to include it.
>
> Just to mention, it is not my habit to answer questions about Wien2k that
> are send directly to me, please use the forum.
>
> Ciao
> Gerhard
>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
>
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Inorganic and Analytical Chemistry
> Johannes Gutenberg - University
> 55099 Mainz
> and
> Max Planck Institute for Chemical Physics of Solids
> 01187 Dresden
> ________________________________________
> Von: tarek.ben-nasr at laposte.net [tarek.ben-nasr at laposte.net]
> Gesendet: Donnerstag, 20. Oktober 2016 14:48
> An: Fecher, Gerhard
> Betreff: Re:Fermi level
>
> Dear Gerhard,
>
> Thank you for your reply but this definition of Fermi level is correct for
> a metal and not for a semiconductor so in band structure putting fermi
> level at the top of valence band is wrong.
>
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-- 
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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