[Pw_forum] The calcualtion of static dielectric constant using espresso!

[Paolo Giannozzi]

On Jun 19, 2007, at 6:42 , Adrain Zhou wrote:

> I just read the definition of dielectric constant from
> http://www.quantum-espresso.org/wiki/index.php/Dielectric_constant.
> I am not sure whether the contribution to dielectric constant from
> clamped-ion polarization corresponds to static response.

what QE calculates is the dielectric tensor at clamped ions
(often referred to as \epsilon_\infty). The ionic contribution
must be calculated and added to this in order to obtain the
static dielectric tensor (\epsilon_0)

>  That is why espresso is unable to deal with dynamics response.

???

> As for the study of temperature effect on the static
> dielectric constant, I am not sure whether what you
> mean is to run MD at fix temperature first and then
> calculate dielectric constant by sampling different
> configurations.

I didn't mean anything like this. The dielectric tensor should
depend upon the temperature via the volume expansion (and
this should be the easy part), but also at constant volume via
anharmonic terms (and this will be less easy).

Paolo
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Paolo Giannozzi, Democritos and University of Udine, Italy