[Pw_forum] why are there two Fermi energies?
Paolo Giannozzi
giannozz at democritos.it
Mon Apr 25 21:22:33 CEST 2011
On Apr 25, 2011, at 15:10 , Eduardo Ariel Menendez Proupin wrote:
>
> >The "two Fermi energies" of the constrained
> >case need not to be exactly the same as the (single)
> >Fermi energy of the unconstrained case, as long as the
> >occupancies for spin-up and spin-down are the same in the
> >two cases.
>
> Why not? Aren't the the energies and occupations related by
> the Fermi-Dirac function?
they are (Fermi-Dirac or whatever function applies), but if you have a
gap and a small broadening, the occupancies will do not (visibly)
depend upon Ef for some interval of values
> 2) tot_magnetization=1
> the spin up/dw Fermi energies are 6.3853 6.1614 ev
> up: 4.8593 4.8594 5.2221 5.2221 5.2221 6.1335 6.1337
> 6.1338
> 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000
> 1.0000 1.0000
Ef=6.3853eV is perfectly consistent with these occupations, as long
as there
are no states between 6.14eV and 6.40eV or so
>
> dw: 4.8796 4.8796 5.2528 5.2530 5.2531 6.1595 6.1596
> 6.1596
> 1.0000 1.0000 1.0000 1.0000 1.0000 0.6715
> 0.6660 0.6625
this is quite the same as case with spin magnetization not set
P.
---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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