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

[Giovani Faccin]

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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 &CONTROL
                 calculation = 'relax' ,
                restart_mode = 'from_scratch' ,
                  wf_collect = .true. ,
                      outdir = './output' ,
                  pseudo_dir = './pseudo/' ,
                      prefix = 'fe2' ,
               etot_conv_thr = 1.0D-6 ,
               forc_conv_thr = 1.0D-4 ,
                     tstress = .false. ,
                     tprnfor = .true. ,
 /
 &SYSTEM
                       ibrav = 1,
                   celldm(1) = 30,
                         nat = 2,
                        ntyp = 2,
                     ecutwfc = 100 ,
                     ecutrho = 1200 ,
                        nbnd = 50,
                 occupations = 'smearing' ,
                     degauss = 0.0005 ,
                    smearing = 'methfessel-paxton' ,
   starting_magnetization(1) = 0.7,
                  lda_plus_u = .false. ,
                Hubbard_U(1) = 1.0d-9,
		Hubbard_U(2) = 1.0d-9,
             assume_isolated = 'none' ,
                    noncolin = .TRUE.,
                   angle1(1) = 0,
                   angle2(1) = 0,
 /
 &ELECTRONS
            electron_maxstep = 2500,
                    conv_thr = 1.0e-8 ,
                 mixing_beta = 0.4 ,
             diagonalization = 'david' ,
 /
 &IONS
 /
ATOMIC_SPECIES
   Fe   55.845  Fe.pbe-nd-rrkjus.UPF
ATOMIC_POSITIONS angstrom 
Fe      1.96       0.000000000    0.000000000    
Fe      0.000000000    0.000000000    0.000000000
K_POINTS {automatic}
1 1 1 1 1 1