[Pw_forum] BiFeO3 problem

[Xunlei Ding]

Hi, Feng,

In crystal unit, 1.433 equals to 0.433. So that's not the reason for
your problem.
And just setting the unit to "alat" is totally wrong.
My suggestion is to use xcrysden to check the structure to see whether
it is the same as you thought.

Hope you will find the correct structure.

Best regards,
Ding

fenghongjian wrote:

> 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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