[QE-users] Iron ibrav=3 bad magnetic moment in a large cell

[Christian helman]

Hi
I'm having a problem with the calculation of a cell with ibrav=-3 (also 3)
I want to do a doping calculation in Fe-BCC, so I start with the unit
cell of the Iron bcc and then i duplicate it.
To start the calculation for the unit cell of iron the parameters i
use (among others) are:
ibrav = -3, celldm(1)= 5.4235161, nat= 1, ntyp= 1, ecutwfc=50,
occupations='smearing', smearing='mp', degauss=0.02,
with only one Fe atom at origin. The pseudopotencial is the PAW type
of Dal Corso.

All works well! correct magnetic moment (2.13) and expected charge density.
Then i duplicate the cell parameter -> celldm(1)=10,8470322 and add
the corresponding atoms (of course nat=8)
ATOMIC_POSITIONS (crystal)
 Fe 0.0 0.0 0.0
 Fe 0.0 0.0 0.5
 Fe 0.0 0.5 0.0
 Fe 0.5 0.0 0.0
 Fe 0.5 0.5 0.5
 Fe 0.5 0.5 0.0
 Fe 0.5 0.0 0.5
 Fe 0.0 0.5 0.5

Except celldm, nat and Kpoints (half of the orginal) the rest of the
input remains unchanged.
At the beginning of the output file, it correctly recognizes the 48
symmetry operations.
But the results are not correct. To start, the magnetic moment and
charges are different for each Fe atom.
I copy part of the output:

Magnetic moment per site  (integrated on atomic sphere of radius R)
     atom   1 (R=0.179)  charge=  6.4398  magn=  1.6308
     atom   2 (R=0.179)  charge=  6.4428  magn=  1.4742
     atom   3 (R=0.179)  charge=  6.4428  magn=  1.4742
     atom   4 (R=0.179)  charge=  6.4428  magn=  1.4742
     atom   5 (R=0.179)  charge=  6.4428  magn=  1.4742
     atom   6 (R=0.179)  charge=  6.4397  magn=  1.6341
     atom   7 (R=0.179)  charge=  6.4397  magn=  1.6341
     atom   8 (R=0.179)  charge=  6.4397  magn=  1.6341

I check the structure with xcrysden, distance and number of neighbours
are correct.
Am I doing something wrong? or there is a bug ?
Thanks in advance

Christian

-- 
Dr. Christian Helman
Div. Física de Superficies - Gerencia de Física
Centro Atómico Bariloche -CNEA
Ezequiel Bustillos 9,500 Km - CP 8400
San Carlos de Bariloche
Provincia de Rio Negro, Argentina
Tel:++54-294-444-5100 int 5375