[Pw_forum] why are there two Fermi energies?

Eduardo Ariel Menendez Proupin eariel99 at gmail.com
Fri Apr 22 17:10:28 CEST 2011

>Shift in eigenvalues can be seen as produced by external magnetic fiels (a
>Zeeman term) then the state with two different Fermi energies may be
thought of a >true ground state with only one Fermi level but in the
presence of this stabilizing >magnetic field proportional to the difference
in Fermi energies.

Why not a true ground state with one Fermi level and an external plus an
internal magnetic field that is due to the spin polarization, causes a shift
ib the KS energies, and is self adjusted to have  thermodynamical
equilibrium, i.e., one Fermi level.

Fixing total magnetization would be equivalent to setting and external
magnetic field, and shifting the eigenvalues would be equivalent to an
internal magnetic field.

By the way, what are the physical restrictions to the values of
tot_magnetization ?
In my system, having 255 electrons, I can fix tehe tot_magnetization  to
0.5, 0.7, 1, 1.2, 1.3, 3.0

For 1.5 <= tot_magnetization<2.5 I get error

     from  set_nelup_neldw  : error #         2
     tot_magnetization is inconsistent with total number of electrons

well I see the restriction is in this piece of code
the restriction is in this code
         if ( ((MOD(NINT(tot_magnetization_),2) == 0) .and.
(MOD(NINT(nelec_),2)==1)) .or.   &
              ((MOD(NINT(tot_magnetization_),2) == 1) .and.
(MOD(NINT(nelec_),2)==0))      ) &
              CALL errore(' set_nelup_neldw ',                          &
             'tot_magnetization is inconsistent with total number of
electrons ', 2 )

I understand that with integer occupations the magnetization could have only
even or odd integer values values depending on the number of electrons. But,
with smearing, allowing real occupations, what is the problem with having
even magnetization with odd number of electrons or close real values?

Best wishes


Eduardo Menendez
Departamento de Fisica
Facultad de Ciencias
Universidad de Chile
Phone: (56)(2)9787439
URL: http://fisica.ciencias.uchile.cl/~emenendez
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