[Pw_forum] BiFeO3 problem

[fenghongjian]

Dear Ding,

       Under R3c (x y z, z x y, y z x, y+1/2 x+1/2 z+1/2, x+1/2 z+1/2 y+1/2, z+1/2 y+1/2 x+1/2 with considering the 60 degree of rotation), Therefore the position {O(6e)(0.538 0.933 0.395) }should be

> 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

Thank you for your kindly discussion.

Best regards
Hongkien Feng




fenghongjian
2007-08-03



发件人： Xunlei Ding
发送时间： 2007-08-03 16:39:48
收件人： PWSCF Forum
抄送： 
主题： Re: [Pw_forum] BiFeO3 problem

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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