[Pw_forum] why don't I get an integer magnetization in a finite system

[Eduardo Ariel Menendez Proupin]

Hi,
I am making calculations for a nanocrystal, isolated system in a supercell,
only gamma point. I have 10 angstrom separation between a nanocrystal border
and the border of the closest image.
 I am a bit surprised to obtain a non integer value of the total
magnetization.

total energy              =   -9085.20537799 Ry
     Harris-Foulkes estimate   =   -9085.20537567 Ry
     estimated scf accuracy    <       0.00001138 Ry

     total magnetization       =     2.79 Bohr mag/cell
     absolute magnetization    =     3.11 Bohr mag/cell

There is not SCF convergence yet, but the restart is waiting in a queue. I
think that the magnetization should be integer.
Should be?
In this case, with an even number of electrons, it should be 0, 2, 4, or 2N.
The reason for getting a non integer magnetization may be
a) supercell not large enough
b) smearing.  occupations = 'smearing', smearing = 'cold', degauss = 0.02,
c) other?

And the solution is
a) Larger supercell
b) fixed occupation, but not if the system is metallic
c) tot_magnetization = 2, ! or any even numbe
d) other

Thanks for the help

Best regards




Eduardo Menendez
Departamento de Fisica
Facultad de Ciencias
Universidad de Chile
Phone: (56)(2)9787439
URL: http://fisica.ciencias.uchile.cl/~emenendez<http://fisica.ciencias.uchile.cl/%7Eemenendez>
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