[Pw_forum] BiFeO3 problem

[fenghongjian]

Dear Ding,

      Thank you very much, I have always visualized the structure using xcrsyden, the structure seems to be right. But the pwscf always could not find the right symmetry group(namely R3C), I am afraid that the input position is not appropriate in some place, unfortunately I couldn't find it so far. You mean the coordinates should  subtract 1 from the original value when it's value exceed 1 in the crystal unit, that is to say the positon is displaced by one unit basis vector. So the same reason the 1.038 is equal to 0.038 in the crystal scheme. Am I right?

    Best regards
   
Hongkien Feng
Physics department,
Beijing university of
aeronautics and astronautics



fenghongjian
2007-08-03



发件人： Xunlei Ding
发送时间： 2007-08-03 04:00:20
收件人： PWSCF Forum
抄送： 
主题： Re: [Pw_forum] BiFeO3 problem

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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