[Pw_forum] Negative value of polarization for doped BaTiO3
Deepashri Saraf
deepashri.saraf at gmail.com
Sat Oct 24 14:07:04 CEST 2015
Dear Users,
I am trying to perform berry phase calculations on pristine as well as
doped BaTiO3 (tetragonal). I get reasonable results for the value of
polarization for pristine BaTiO3.
------------------------------------------------------------------------------------------------------------------------
SUMMARY OF PHASES
~~~~~~~~~~~~~~~~~
Ionic Phase: -0.12600 (mod 2)
Electronic Phase: 0.40671 (mod 2)
TOTAL PHASE: 0.28071 (mod 2)
VALUES OF POLARIZATION
~~~~~~~~~~~~~~~~~~~~~~
The calculation of phases done along the direction of vector 3
of the reciprocal lattice gives the following contribution to
the polarization vector (in different units, and being Omega
the volume of the unit cell):
P = 2.1352035 (mod 15.2130988) (e/Omega).bohr
P = 0.0049373 (mod 0.0351775) e/bohr^2
P = 0.2822719 (mod 2.0111573) C/m^2
The polarization direction is: ( 0.00000 , 0.00000 , 1.00000 )
------------------------------------------------------------------------------------------------------------------------
But in case of doped BaTiO3, I get negative value of polarization. I used a
2x2x3 supercell for these calculations.
-------------------------------------------------------------------------------------------------------------------------
SUMMARY OF PHASES
~~~~~~~~~~~~~~~~~
Ionic Phase: -0.50398 (mod 2)
Electronic Phase: -0.37438 (mod 2)
TOTAL PHASE: -0.87836 (mod 2)
VALUES OF POLARIZATION
~~~~~~~~~~~~~~~~~~~~~~
The calculation of phases done along the direction of vector 3
of the reciprocal lattice gives the following contribution to
the polarization vector (in different units, and being Omega
the volume of the unit cell):
P = -19.9950561 (mod 45.5280337) (e/Omega).bohr
P = -0.0038804 (mod 0.0088355) e/bohr^2
P = -0.2218486 (mod 0.5051413) C/m^2
The polarization direction is: ( 0.00000 , 0.00000 , 1.00000 )
--------------------------------------------------------------------------------------------------------------------------
I also tried using a finer k-mesh, but landed up with the same value of
polarization. Does the negative polarization have any physical meaning or
is it a numerical error?
Any help appreciated. Thanks in advance.
Best,
DS.
--
Deepashri Saraf
PhD Student
Department of Physics, SPPU
Pune (India)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20151024/f60f0302/attachment.html>
More information about the users
mailing list