# [Pw_forum] Which dielectric constant is calculated

Marcel Mohr marcel at physik.tu-berlin.de
Thu Sep 20 20:13:44 CEST 2007

Dear list-members

during a PHONON calculation of a polar crystal, the dielectric constant is
calculated and written to the dynamical matrix.
With this and dynmat the LO TO splitting can be calculated.
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.
But this one is not for frequencies like visible light? (like
\epsilon_\infty in experimental books, like, e.g., in Landolt-Boernstein)

I am grateful for any hints

Best regards
Marcel

________________________________________________________________________
Marcel Mohr			Institut für Festkörperphysik, TU Berlin
marcel(at)physik.tu-berlin.de	Sekr. PN 5-4
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