<div dir="ltr"><div><div><div> Thanks for your response Paolo. I did exactly as you said, I used dynmat.x . I think the asymetry comes from Eq. (2) of Fennie&Rabe due to having a different frequency, or from eq (3) due to having a different eigenvector. In fact, when I specify no direction with the vector q(i), I get three equal frecuencies and equal components for the dielectric tensor. Looking at the eigenvectors, I think the asymetry comes from Eq. 2. I made a simple calculation with the following data<br><br><br># mode [cm-1] [THz] IR<br> 1 -0.00 -0.0000 0.0000<br> 2 0.00 0.0000 0.0000<br> 3 0.00 0.0000 0.0000<br> 4 133.01 3.9875 2.3657<br> 5 133.01 3.9875 2.3657<br> 6 154.23 4.6238 2.3657<br><br>Electronic dielectric permittivity tensor (F/m units)<br> 11.387818 0.000000 -0.000000<br> 0.000000 11.387818 -0.000000<br> 0.000000 0.000000 11.387818<br><br> ... with zone-center polar mode contributions<br> 14.306543 0.000000 0.000000<br> 0.000000 15.312431 -0.000000<br> 0.000000 -0.000000 15.312431<br><br> freq ( 6) = 4.623845 [THz] = 154.234861 [cm-1]<br> ( -0.750355 0.000000 0.000000 0.000000 -0.000000 0.000000 )<br> ( 0.661035 -0.000000 -0.000000 0.000000 0.000000 -0.000000 )<br><br>Only the 6th eigenvector has component in axis 1. A very simple calculation shows that you are right, regarding Eq (2) I just need to correct the omega_m from 154 to 133 cm^-1<br><br>[emenendez@leftraru2 VC-relax]$ echo '11.387818+(15.312431-11.387818)'|bc -l<br>15.312431<br>[emenendez@leftraru2 VC-relax]$ echo '11.387818+(15.312431-11.387818)*(133.01/154.23)^2'|bc -l<br>14.30677507068329634588<br><br></div>So, is this an error ? <br><br></div>Thank you again<br></div>Eduardo<br><div><div><div><br> <br><br><br><br><br><div><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">---------- Mensaje reenviado ----------<br>From: Paolo Giannozzi <<a href="mailto:p.giannozzi@gmail.com" target="_blank">p.giannozzi@gmail.com</a>><br>To: PWSCF Forum <<a href="mailto:pw_forum@pwscf.org" target="_blank">pw_forum@pwscf.org</a>><br>Cc: <br>Date: Mon, 11 Jan 2016 21:51:24 +0100<br>Subject: Re: [Pw_forum] non-cubic dielectric tensor in a cubic crystal.<br><div dir="ltr"><div><div><div>Hi Eduardo<br><br></div>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):<br> ! Algorithm from Fennie and Rabe, Phys. Rev. B 68, 18411 (2003)<br></div>My guess is that the algorithm assumes TO frequencies only, but LO frequencies are used instead since you specified a direction for q=>0.<br><br></div>Paolo<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Jan 11, 2016 at 8:10 PM, Eduardo Menendez <span dir="ltr"><<a href="mailto:eariel99@gmail.com" target="_blank">eariel99@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div><div>Hi, <br><br>I am computing the dielectric funciton of a cubic material (CdTe). <br></div>I am surprised that the to see a result like this the dielectric tensor below: <br><br># mode [cm-1] [THz] IR<br> 1 0.00 0.0000 0.0000<br> 2 0.00 0.0000 0.0000<br> 3 0.00 0.0000 0.0000<br> 4 133.01 3.9875 2.3657<br> 5 133.01 3.9875 2.3657<br> 6 154.23 4.6238 2.3657<br><br>Electronic dielectric permittivity tensor (F/m units)<br> 11.387818 0.000000 -0.000000<br> 0.000000 11.387818 -0.000000<br> 0.000000 0.000000 11.387818<br><br> ... with zone-center polar mode contributions<br></div> 14.306543 0.000000 -0.000000 (HERE IS ACKWARD)<br><div> 0.000000 15.312431 -0.000000<br> -0.000000 -0.000000 15.312431<br><br><div>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. <br><br></div><div><div>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. <br><br></div><div>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 ? <br><br></div><div>Thank you, <br></div><div><br clear="all"><div><div><div dir="ltr"><div><div dir="ltr">
<div>Eduardo Menendez Proupin<br>Departamento de Fisica, Facultad de Ciencias, Universidad de Chile <br>URL: <a href="http://www.gnm.cl/emenendez" target="_blank">http://www.gnm.cl/emenendez</a></div><br></div></div></div></div></div></div></div></div></div></blockquote></div></div>
</blockquote></div><br></div></div></div></div></div></div>