# [Pw_forum] Which dielectric constant is calculated

Paolo Giannozzi giannozz at nest.sns.it
Thu Sep 20 22:38:46 CEST 2007

On Sep 20, 2007, at 20:13 , Marcel Mohr wrote:

> Is this dielectric constant the static one, or the high-frequency
> one (\epsilon_\infty)?
>
> I am confused, because in the paper from Gianozzi et al. PRB 43
> 7231, in formula (18) where the non-analytic part of the dynamical
> matrix is calculated, a  \epsilon\infty enters which is called the
> high-frequency static dieelectric tensor.

this answers your question: it is both ! Seriously: it is the
dielectric tensor at frequencies that are high with respect
to phonon modes, but low wrt electronic excitations. So it
is "static" wrt the latter and "high-frequency" wrt the former.

Paolo
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Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
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