[Pw_forum] BiFeO3 problem

[Xunlei Ding]

Dear Feng,

There is no difference whether you input 1.038 or 0.038.
You can try it by using xcrysden to see the structure.
Now your structrue is:
> 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
But why not:
O 0.53800 0.93300 0.39500
O 0.39500 0.53800 0.93300
O 0.93300 0.39500 0.53800
O 1.03800 1.43300 0.89500
O 0.89500 1.03800 1.43300
O 1.43300 0.89500 1.03800
I am not familar with BiFeO3 and R3c. So I am not sure about that.

Another question is: whether R3c symmetry is included in PWSCF, or
whether "c" can be recognized by PWSCF.

Best regards,
Ding



fenghongjian wrote:

> 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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