[Pw_forum] Relation between cell magnetization and atomic magnetization in the non-collinear calculation

[Guido Fratesi]

Dear Giovani,

the unit cell is not 100% filled by the atom-centered spheres where the 
quantities of your interest are computed. Notice that also the sum of 
the atomic charges (11) is different than the cell one (16?).

For information about such spheres, you might want to have a look in the 
output file to something like:

      Generating pointlists ...
      new r_m :   0.3457 (alat units)  1.8649 (a.u.) for type    1

and the subroutine in PW/make_pointlists.f90. From that file:

   ! This initialization is needed in order to integrate charge (or
   ! magnetic moment) in a sphere around the atomic positions.
   ! This can be used to simply monitor these quantities during the scf
   ! cycles or in order to calculate constrains on these quantities.
   !
   ! If the integration radius r_m is not provided in input, it is
   ! calculated here. The integration is a sum over all points in real
   ! space with the weight 1, if they are closer than r_m to an atom
   ! and 1 - (distance-r_m)/(0.2*r_m) if r_m<distance<1.2*r_m

HTH,
Guido

Il 01/09/2012 01:49 PM, Giovani Faccin ha scritto:
> Dear PW-Users,
>
> While performing a test calculation for a non-collinear Fe2 dimer
> without spin-orbit, I get the following results (just printing the
> relevant part):
>
>
> ==============================================================================
>       atom number    1 relative position :    0.1234   0.0000   0.0000
>       charge :     5.500331
>       magnetization :          0.000000    0.000000    2.549039
>       magnetization/charge:    0.000000    0.000000    0.463434
>       polar coord.: r, theta, phi [deg] :     2.549039    0.000000
> 360.000000
>
>   ==============================================================================
>
>   ==============================================================================
>       atom number    2 relative position :    0.0001   0.0000   0.0000
>       charge :     5.500187
>       magnetization :          0.000000    0.000000    2.548980
>       magnetization/charge:    0.000000    0.000000    0.463435
>       polar coord.: r, theta, phi [deg] :     2.548980    0.000000
> 360.000000
>
>   ==============================================================================
>
> (little more output here, then)
>
>      total magnetization       =     0.00     0.00     6.00 Bohr mag/cell
>       absolute magnetization    =     6.36 Bohr mag/cell
>
>
> The cell magnetization prints 6.0 Bohr/cell, which is the expected
> result. However, the atomic magnetization prints 2.549039 + 2.548980 ~
> 5.10 mB.
>
> I'm wondering: why is not the atomic magnetization sum equal (or very
> close to) the cell magnetization? If needed, the input file is attached.
>
> Thanks in advance.
>
> Giovani Faccin
> UFMS / Brazil
>
>
>
>
>
>
>
>
> Giovani
>
>
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-- 
Guido Fratesi

Dipartimento di Scienza dei Materiali
Universita` degli Studi di Milano-Bicocca
via Cozzi 53, 20125 Milano, Italy