[Pw_forum] negative value of polarization and Z* for Pb in Tetragonal PbTiO3 and discrepancy in calculation of
sathya subramanyan
sathya_sheela1985001 at rediffmail.com
Fri Jun 27 11:51:12 CEST 2008
Dear Developers,
I am trying to calculate the Berry Phaze Polarization and effective charge on Pb(with the displacement of .01*ao) for PbTiO3(tetragonal) but am getting a negative value, using quantum espresso ver 4.0.
When I run the example 10 for cubic phase the polarization and the Z* comes out to be alright. But, when I try for tetragonal phase, I am getting negative ionic phase leading to negative polarization for Pb.
If I compare the out put file for both cubic and tertragonal phase, to my surprise in the cubic phase the total ionic phase comes out to be positive (actually, if you sum it is negative), where as in the case of tetragonal phase the ionic phase comes out to be negative (but, it is positive if you sum the same way as for the cubic).
I do not understand this differrent summing rule for different phases. I am attaching both the input and out files for cubic and tetragonal phases. I would appreciate any useful suggestions to clear this point.
I am very sorry for the long mail and data files.
INPUT FILE FOR CUBIC PbTiO34
&control
calculation = 'nscf'
pseudo_dir = '/home/nbaski/espresso-4.0/pseudo/'
outdir = '/home/nbaski/tmp/'
lberry = .true.
gdir = 3
nppstr = 7
/
&system
ibrav = 1
celldm(1) = 7.3699
nat = 5
ntyp = 3
nbnd = 22
ecutwfc = 30.0
occupations = 'fixed'
degauss = 0.00
/
&electrons
conv_thr = 1e-5
mixing_beta = 0.3
/
ATOMIC_SPECIES
Pb 207.2 Pb.vdb.UPF
Ti 47.867 Ti.vdb.UPF
O 15.9994 O.vdb.UPF
ATOMIC_POSITIONS
Pb 0.000 0.000 0.010
Ti 0.500 0.500 0.500
O 0.000 0.500 0.500
O 0.500 0.500 0.000
O 0.500 0.000 0.500
K_POINTS {automatic}
4 4 7 1 1 1
THE O/P FILE FOR CUBIC PbTiO3 (as it is a very big file am attaching only the ionic phase calculation section)
==================================================
POLARIZATION CALCULATION
!!! NOT THOROUGHLY TESTED !!!
--------------------------------------------------
K-POINTS STRINGS USED IN CALCULATIONS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
G-vector along string (2 pi/a): 0.00000 0.00000 1.00000
Modulus of the vector (1/bohr): 0.85255
Number of k-points per string: 7
Number of different strings : 3
IONIC POLARIZATION
~~~~~~~~~~~~~~~~~~
Note: (mod 1) means that the phases (angles ranging from
-pi to pi) have been mapped to the interval [-1/2,+1/2) by
dividing by 2*pi; (mod 2) refers to the interval [-1,+1)
============================================================================
Ion Species Charge Position Phase
----------------------------------------------------------------------------
1 Pb 14.000 0.0000 0.0000 0.0100 0.14000 (mod 2)
2 Ti 12.000 0.5000 0.5000 0.5000 0.00000 (mod 2)
3 O 6.000 0.0000 0.5000 0.5000 -1.00000 (mod 2)
4 O 6.000 0.5000 0.5000 0.0000 0.00000 (mod 2)
5 O 6.000 0.5000 0.0000 0.5000 -1.00000 (mod 2)
----------------------------------------------------------------------------
IONIC PHASE: 0.14000 (mod 2)
============================================================================
ELECTRONIC POLARIZATION
~~~~~~~~~~~~~~~~~~~~~~~
Note: (mod 1) means that the phases (angles ranging from
-pi to pi) have been mapped to the interval [-1/2,+1/2) by
dividing by 2*pi; (mod 2) refers to the interval [-1,+1)
============================================================================
Spin String Weight First k-point in string Phase
----------------------------------------------------------------------------
up 1 0.250000 0.1250 0.1250 -0.5000 -0.05427 (mod 1)
up 2 0.500000 0.1250 0.3750 -0.5000 -0.04876 (mod 1)
up 3 0.250000 0.3750 0.3750 -0.5000 -0.05048 (mod 1)
----------------------------------------------------------------------------
down 1 0.250000 0.1250 0.1250 -0.5000 -0.05427 (mod 1)
down 2 0.500000 0.1250 0.3750 -0.5000 -0.04876 (mod 1)
down 3 0.250000 0.3750 0.3750 -0.5000 -0.05048 (mod 1)
----------------------------------------------------------------------------
Average phase (up): -0.05057 (mod 1)
Average phase (down): -0.05057 (mod 1)
ELECTRONIC PHASE: -0.10114 (mod 2)
============================================================================
SUMMARY OF PHASES
~~~~~~~~~~~~~~~~~
Ionic Phase: 0.14000 (mod 2)
Electronic Phase: -0.10114 (mod 2)
TOTAL PHASE: 0.03886 (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 = 0.2864184 (mod 14.7398000) (e/Omega).bohr
P = 0.0007155 (mod 0.0368220) e/bohr^2
P = 0.0409070 (mod 2.1051744) C/m^2
The polarization direction is: ( 0.00000 , 0.00000 , 1.00000 )
==================================================
THE I/P FILE FOR TETRAGONAL PbTiO3
&CONTROL
calculation = 'nscf'
pseudo_dir = '/home/nbaski/espresso-4.0/pseudo/'
outdir = '/home/nbaski/tmp/'
lberry = .true.
gdir = 3
nppstr = 7
/
&SYSTEM
ibrav = 6
celldm(1) = 7.3415
celldm(3) = 1.0653
nat = 5
ntyp = 3
nbnd = 22
ecutwfc = 30.0
occupations = 'fixed'
degauss = 0.00
/
&ELECTRONS
conv_thr = 1e-5
mixing_beta = 0.3
/
ATOMIC_SPECIES
Pb 207.2 Pb.vdb.UPF
Ti 47.867 Ti.vdb.UPF
O 15.9994 O.vdb.UPF
ATOMIC_POSITIONS
Pb 0.00000 0.00000 0.01000
Ti 0.50000 0.50000 0.53770
O 0.50000 0.50000 0.11180
O 0.00000 0.50000 0.61740
O 0.50000 0.00000 0.61740
K_POINTS {automatic}
4 4 7 1 1 1
O/P FILE FOR PbTiO3
==================================================
POLARIZATION CALCULATION
!!! NOT THOROUGHLY TESTED !!!
--------------------------------------------------
K-POINTS STRINGS USED IN CALCULATIONS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
G-vector along string (2 pi/a): 0.00000 0.00000 0.93870
Modulus of the vector (1/bohr): 0.80338
Number of k-points per string: 7
Number of different strings : 3
IONIC POLARIZATION
~~~~~~~~~~~~~~~~~~
Note: (mod 1) means that the phases (angles ranging from
-pi to pi) have been mapped to the interval [-1/2,+1/2) by
dividing by 2*pi; (mod 2) refers to the interval [-1,+1)
============================================================================
Ion Species Charge Position Phase
----------------------------------------------------------------------------
1 Pb 14.000 0.0000 0.0000 0.0100 0.13142 (mod 2)
2 Ti 12.000 0.5000 0.5000 0.5377 0.05689 (mod 2)
3 O 6.000 0.5000 0.5000 0.1118 0.62968 (mod 2)
4 O 6.000 0.0000 0.5000 0.6174 -0.52267 (mod 2)
5 O 6.000 0.5000 0.0000 0.6174 -0.52267 (mod 2)
----------------------------------------------------------------------------
IONIC PHASE: -0.22735 (mod 2)
============================================================================
ELECTRONIC POLARIZATION
~~~~~~~~~~~~~~~~~~~~~~~
Note: (mod 1) means that the phases (angles ranging from
-pi to pi) have been mapped to the interval [-1/2,+1/2) by
dividing by 2*pi; (mod 2) refers to the interval [-1,+1)
============================================================================
Spin String Weight First k-point in string Phase
----------------------------------------------------------------------------
up 1 0.250000 0.1250 0.1250 -0.4694 -0.30118 (mod 1)
up 2 0.500000 0.1250 0.3750 -0.4694 -0.28922 (mod 1)
up 3 0.250000 0.3750 0.3750 -0.4694 -0.25437 (mod 1)
----------------------------------------------------------------------------
down 1 0.250000 0.1250 0.1250 -0.4694 -0.30118 (mod 1)
down 2 0.500000 0.1250 0.3750 -0.4694 -0.28922 (mod 1)
down 3 0.250000 0.3750 0.3750 -0.4694 -0.25437 (mod 1)
----------------------------------------------------------------------------
Average phase (up): -0.28353 (mod 1)
Average phase (down): -0.28353 (mod 1)
ELECTRONIC PHASE: -0.56706 (mod 2)
============================================================================
SUMMARY OF PHASES
~~~~~~~~~~~~~~~~~
Ionic Phase: -0.22735 (mod 2)
Electronic Phase: -0.56706 (mod 2)
TOTAL PHASE: -0.79441 (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 = -6.2130096 (mod 15.6417999) (e/Omega).bohr
P = -0.0147393 (mod 0.0371074) e/bohr^2
P = -0.8426689 (mod 2.1214933) C/m^2
The polarization direction is: ( 0.00000 , 0.00000 , 1.00000 )
==================================================
Thank you in advance for any help
SATHYA SHEELA.S
Grad. Student
Department of Physics
National Institute of Technology
Tiruchirapalli - 620015
India
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.democritos.it/pipermail/pw_forum/attachments/20080627/757fde5c/attachment-0001.htm
More information about the Pw_forum
mailing list