[Pw_forum] polarization spin versus non-spin

[Nossa, Javier]

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>
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