PPA+BSE for metalls

[samaneh]

Dear Developers,
I have done some G0W0 calculation
with PPA approximation (I changed the default value of PPA imaginary frequency).
Actually my system is a semiconductor
which is doped by some light elements (e.g. H)
and become metallic!
The Band structure calculated
with G0W0(PPA) is in a very good
agreement with PBE calculation.
So, I did BSE calculation on top of that
and plot the EELS.
The plasma frequency is 4 eV for the system
and there is a peak in EELS at around 2 eV!
Does it mean that the PPA is not good
for this system??
Thank you in advance

[Daniele Varsano]

Dear S. Aitei,
the plasma frequency in PPA is a parameter of an approximation (plasmon pole approximation indeed) needed to model the frequency dependence of the dielectric matrix to be used in the GW calculation, so it is not related with the Drude plasma frequency of a metal. Note the plasma frequency in PPA it is an imaginary frequency.
BSE kernel instead is calculated considering a static dielectric matrix, and only the zero frequency of the PPA calculation is read and used to build the kernel.
If you want to include Drude contribution you need to define the Drude plasmon frequency defined by
DrudeWBS

Best,

Daniele