Dear QE users,
I am a PhD student working with Berry phase theory of polarization
calculations of single layer 2D material hBN in quantum espresso (applying
vacuum in the z-direction).
I found -0.0000002 C/m^2 polarization from lberry=.true. in QE; however,
total phases belonging to electronic and ionic contributions are found as
equal to each other and given as 0.40381 and -0.40381 with 5 significant
digits.
Is it OK to take -0.0000002 C/m^2 as the polarization of the system? or Is
this a numerical error?
Also, when I change the dimension of the unit cell in z-direction and
position of the material inside the cell, this polarization value changes
even though I use the same material.
Are all those numerical errors or physical phenomena because I know that
there are vacuum fluctuations and Lamb modes, and so on? Can we probe those
with QE?
I look forward to hearing from you soon.
Best regards,
Aykut Turfanda
PhD student at Istanbul Technical University
###############################
SUMMARY OF PHASES
~~~~~~~~~~~~~~~~~
Ionic Phase: -0.40381
Electronic Phase: 0.40381
TOTAL PHASE: -0.00000 MOD_TOT: 1
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 = -0.0000030 (mod 40.7880378) (e/Omega).bohr
P = -0.0000000 (mod 0.0514003) e/bohr^2
P = -0.0000002 (mod 2.9386420) C/m^2
The polarization direction is: ( 0.00000 , 0.00000 , 1.00000 )
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