[Pw_forum] BiFeO3 problem

[fenghongjian]

Dear PWSCF users,

     I'm trying to calculate the electronic properties of rhombohedral BiFeO3 under R3C 

symmetry group. The wychoff position is Bi(2b)(0 0 0),Fe(2a)(0.221 0.221 0.221),O(6e)(0.538 

0.933 0.395), hence under R3C group symmetry the atomic position should be
Bi       0.00000   0.00000  0.00000
Bi       0.50000   0.50000  0.50000
Fe       0.22100   0.22100  0.22100
Fe       0.72100     0.72100     0.72100   
O        0.53800      0.93300     0.39500
O        0.39500     0.53800     0.93300
O        0.93300     0.39500     0.53800
O        1.43300     1.03800      0.89500
O        1.03800     0.89500    1.43300 
O        0.89500     1.43300      1.03800

When I set the ATOMIC_POSITIONS in alat unit the code gave no symmetry, and the code 

produced wrong symmertry ( not R3c group) with the ATOMIC_POSITIONS in crystal unit.

Acturally in crystal unit the triplet coordinates should be less than 1, but in my case the 

1.433 was obviously wrong, but O(6e)(0.538 0.933 0.395) under R3C will definitely produce 

the value above. I have encountered this problem for a long time, could anyone point the 

wrong place in my case? Any sugestions will be very appreciated.

My input file was pasted below:
&control
calculation='scf'
restart_mode='from_scratch',
verbosity='high',
prefix='bifo',
pseudo_dir='./',
outdir='./'
/
 &system
ibrav= 5, celldm(1)= 10.6427, celldm(4)= 0.5, nat= 10, ntyp= 3,
ecutwfc=35.0
occupations = 'fixed'
degauss=0.00
nbnd=100
lda_plus_u=.true. Hubbard_U(2)=5,
nspin=2,multiplicity=5,
/
 &electrons
mixing_beta=0.3,
diagonalization='cg'
/
ATOMIC_SPECIES
Bi 208.98   Bi.pbe-d-mt.UPF
Fe 55.847   Fe.pbe-sp-van_ak.UPF
O 15.999    O.pbe-van_ak.UPF
ATOMIC_POSITIONS  {alat}
Bi       0.00000   0.00000  0.00000
Bi       0.50000   0.50000  0.50000
Fe       0.22100   0.22100  0.22100
Fe       0.72100     0.72100     0.72100   
O        0.53800      0.93300     0.39500
O        0.39500     0.53800     0.93300
O        0.93300     0.39500     0.53800
O        1.43300     1.03800      0.89500
O        1.03800     0.89500    1.43300 
O        0.89500     1.43300      1.03800
K_POINTS {automatic}
8 8 8 0 0 0 

Best Regards,


Hongkien Feng

Physics department,
Beijing university of 
aeronautics and astronautics





fenghongjian
2007-08-02
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