[Pw_forum] non-cubic dielectric tensor in a cubic crystal.

Paolo Giannozzi p.giannozzi at gmail.com
Tue Jan 12 17:23:56 CET 2016

On Mon, Jan 11, 2016 at 11:37 PM, Mostafa Youssef <myoussef at mit.edu> wrote:

> I also get a non-cubic dielectric tensor for cubic semiconductors when I
> allow the computation of the nonanalytic terms by specifying a q-vector and
> q is not equal 0.  But I do not fully understand what is going on here.  I
> think (but not very sure) if you do not specify q then you actually
> calculate the nonanalytic terms for q->0

you actually calculate only the "analytic" terms for q=0. There are no
nonanalytic terms if no direction for q is specified.

> and then you recover the correct cubic tensor with zone center phonons
> contribution.
> On the other hand calculating epsilon_0 by applying electric field and
> relaxing the ions yields a reasonable cubic dielectric tensor.
> I hope somebody can help in clarifying this.

not sure I have clarified anything; I just added a check so that if someone
tries to compute the phonon contribution to the the dielectric tensor with
TO-LO splitting on, a warning message is printed.


> Mostafa Youssef
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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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