Hi Eduardo you used dynmat.x, didn't you? the \epsilon_0 tensor is computed is subroutine polar_mode_permittivity of PHonon/PH/dynmat.f90. The header mentions a nonexistent reference (the correct page number should be 184111): ! Algorithm from Fennie and Rabe, Phys. Rev. B 68, 18411 (2003) My guess is that the algorithm assumes TO frequencies only, but LO frequencies are used instead since you specified a direction for q=>0.
Paolo On Mon, Jan 11, 2016 at 8:10 PM, Eduardo Menendez <[email protected]> wrote: > 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” > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > -- Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
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