[Pw_forum] polarization spin versus non-spin

[Mojtaba Mirseraji]

Dear Javier

You say the polarization of BaTiO3 (non-spin polarized) is
P=-0.334019. and you say that it is correct.
But I read in several articles that they report P is about +0.25 to
+0.29 C/m^2. (Tetragonal !!!)
Why?
Meanwhile, I could not calculate it, even in the relaxed structure, my
polarization and lattice parameters of tetragonal BaTiO3 are not the
same as reported.
Can you help me?

Regards

Mojtaba Mirseraji
Ph.d Candidate
Physics Group
Arak University
I.R.IRAN

On 2/20/15, Nossa, Javier <jnossa at carnegiescience.edu> wrote:
> Thank you very much for your reply Andrei.
>
> On Fri, Feb 20, 2015 at 10:45 AM, Andrei Malashevich <
> andrei.malashevich at yale.edu> wrote:
>
>> Dear Javier,
>>
>> For spin-polarized case, you have 0.6698526-1.0038673=-0.3340147,
>> value very similar to the spin unpolarized case.
>> Polarization is defined only modulo a quantum, and in the above, I just
>> subtracted the quantum.
>>
>> Andrei
>>
>>
>> On Fri, Feb 20, 2015 at 10:27 AM, Nossa, Javier <
>> jnossa at carnegiescience.edu> wrote:
>>
>>> Dear pwscfers,
>>> I am calculating the polarization of BaTiO3 and found a different value
>>> of it when implementing spin-polarized, nspin=2.
>>>
>>> non-spin-polarized gives P=-0.3340199 (mod 2.0077346) C/m^2, which is
>>> correct.
>>> spin-polarized gives P=0.6698526 (mod 1.0038673)  C/m^2, which is not
>>> correct.
>>>
>>> Although it seems to be just a factor of two difference in the absolute
>>> value of the polarization, it is not exactly a factor of two. It is
>>> 2.0054...
>>> In addition, the sign of the polarization is opposite.
>>> On the other hand, the mod is exactly a factor of two.
>>>
>>> Why there is such a difference in the polarization?
>>>
>>> I am doing this as a test because my real system is magnetic and bigger
>>> than BaTiO3.
>>>
>>> Here are the inputs for the nscf calculation:
>>>
>>> spin-polarized:
>>> &control
>>>     calculation='nscf'
>>>     restart_mode='from_scratch',
>>>     prefix='job',
>>>     lberry        = .true.
>>>     gdir          = 3
>>>     nppstr        = 10
>>>  /
>>> &system
>>>     ibrav= 0,
>>>     celldm(1)=1.0,
>>>     nat=  5, ntyp= 3,
>>>     ecutwfc = 120,
>>>     !occupations='smearing', smearing='gauss', degauss=0.003,
>>>     !occupations='fixed',
>>>     input_dft='wc'
>>>     nspin=2,
>>>     tot_magnetization= 0.0,
>>> /
>>> &electrons
>>> /
>>> ATOMIC_SPECIES
>>>  Ba  137.327 Ba.wc-n-nc.UPF
>>>  Ti  47.867 Ti.wc-n-nc.UPF
>>>   O  15.9994 O.wc-nc.UPF
>>> CELL_PARAMETERS (alat=1.0)
>>>  7.54662 0.0 0.0
>>>  0.0 7.54662 0.0
>>>  0.0 0.0 7.74409
>>> ATOMIC_POSITIONS {crystal}
>>> Ba      0.00000 0.00000 0.00000
>>> Ti      0.50000 0.50000 0.48186
>>> O       0.00000 0.50000 0.51791
>>> O       0.50000 0.00000 0.51791
>>> O       0.50000 0.50000 0.03133
>>> K_POINTS {automatic}
>>> 4 4 4 0 0 0
>>>
>>>
>>> non-spin-polarized:
>>> &control
>>>     calculation='nscf'
>>>     restart_mode='from_scratch',
>>>     prefix='job',
>>>     lberry        = .true.
>>>     gdir          = 3
>>>     nppstr        = 10
>>>  /
>>> &system
>>>     ibrav= 0,
>>>     celldm(1)=1.0,
>>>     nat=  5, ntyp= 3,
>>>     ecutwfc = 120,
>>>     !occupations='smearing', smearing='gauss', degauss=0.003,
>>>     !occupations='fixed',
>>>     input_dft='wc'
>>> /
>>> &electrons
>>> /
>>> ATOMIC_SPECIES
>>>  Ba  137.327 Ba.wc-n-nc.UPF
>>>  Ti  47.867 Ti.wc-n-nc.UPF
>>>   O  15.9994 O.wc-nc.UPF
>>> CELL_PARAMETERS (alat=1.0)
>>>  7.54662 0.0 0.0
>>>  0.0 7.54662 0.0
>>>  0.0 0.0 7.74409
>>> ATOMIC_POSITIONS {crystal}
>>> Ba      0.00000 0.00000 0.00000
>>> Ti      0.50000 0.50000 0.48186
>>> O       0.00000 0.50000 0.51791
>>> O       0.50000 0.00000 0.51791
>>> O       0.50000 0.50000 0.03133
>>> K_POINTS {automatic}
>>> 4 4 4 0 0 0
>>>
>>>
>>> Pseudopotentials are taken from THEOS PSLibrary 0.3.1.
>>>
>>> Outputs are attached.
>>>
>>>
>>> Thank you very much for your help.
>>>
>>> --
>>> With best regards,
>>> Javier Francisco Nossa
>>>
>>> Postdoc at Geophysical Laboratory
>>> Carnegie Institution of Washington
>>> 5251 Broad Branch Road, N.W.
>>> Washington, DC 20015-1305
>>> Tel.: 1.240.476.3993
>>> E-mail: jnossa at carnegiescience.edu <dappleby at ciw.edu>
>>>
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>>>
>>
>>
>>
>> --
>> Andrei Malashevich
>> Postdoctoral Associate
>> Center for Research on Interface Structures and Phenomena
>> Department of Applied Physics
>> Yale University
>>
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>
>
>
> --
> With best regards,
> Javier Francisco Nossa
>
> Postdoc at Geophysical Laboratory
> Carnegie Institution of Washington
> 5251 Broad Branch Road, N.W.
> Washington, DC 20015-1305
> Tel.: 1.240.476.3993
> E-mail: jnossa at carnegiescience.edu <dappleby at ciw.edu>
>