[Pw_forum] non-cubic dielectric tensor in a cubic crystal.
Eduardo Menendez
eariel99 at gmail.com
Mon Jan 11 20:10:42 CET 2016
Hi,
I am computing the dielectric funciton of a cubic material (CdTe).
I am surprised that the to see a result like this the dielectric tensor
below:
# mode [cm-1] [THz] IR
1 0.00 0.0000 0.0000
2 0.00 0.0000 0.0000
3 0.00 0.0000 0.0000
4 133.01 3.9875 2.3657
5 133.01 3.9875 2.3657
6 154.23 4.6238 2.3657
Electronic dielectric permittivity tensor (F/m units)
11.387818 0.000000 -0.000000
0.000000 11.387818 -0.000000
0.000000 0.000000 11.387818
... with zone-center polar mode contributions
14.306543 0.000000 -0.000000 (HERE IS ACKWARD)
0.000000 15.312431 -0.000000
-0.000000 -0.000000 15.312431
I (guess that) undertand the first tensor above as \epsilon_{\infty}, and
the second tensor as \epsilon_0. Why is the first component 14.3 different
from the others 15.31, shouldn't it be a diagonal tensor ? 15.31 is
consistent with epsilon_infty and the Lyddane-Sachs-Teller formula.
Well, I set q(1)=1, q(2)=0,q(3)=0, so I guess the component 11 is a
longitudinal dielectric constant. I see that changing the vector q also
change the tensor However, I think that for an LO phonon the electric
displacement is 0, so is null the longitudinal dielectric constant.
Sorry, I did never see this in textbooks. Finally, and practically, if
14.3 is a longitudinal dielectric constant, is this the dielectric constant
that screens a static constant electric field ?
Thank you,
Eduardo Menendez Proupin
Departamento de Fisica, Facultad de Ciencias, Universidad de Chile
URL: http://www.gnm.cl/emenendez
“No cometerás actos impuros ni publicarás en revistas open-acces”
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