on RPA for metallic systems

[Stephan]

Hello,
It is definitely not understandable for me what to insert in DrudeWXd.
I whant to calculate the optical response for BaFe2As2. It's a metall, so I need to insert a complex Drude frequency. In Andrea Marini's PhD-Theses pages 137-138
I read that the real part can be calculated from the fermi-k-vector, so I suppose that I can use the fermi-energy received in pwscf to calculate the real part. Am I right or must I use experimental data?
But what do I have to choose for this delta in A-19 which is obviously the imaginary part of the plasma frequency.
If I have to use experimental date, how do I extract real and imaginary part of the plasma-frequency from data (lets say reflectivity measurments or optical conductivity)?
Please help. I'm at the end of my wits...

Thanks and regards
Stephan

[Daniele Varsano]

Dear Stephan,
let me first ask you to fill your signature with your complete affiliation. This is a rule of the forum.
In Yambo the intraband contribution is implemented via the Drude model, and yes you need input the plasma frequency as the ab-initio calculation it is not
in the code anymore and as you can see fro the Andrea Marini thesis it requires an enormous number of k point sampling.
The best think to do is to input experimental data if available (the equation you are mentioning are taken frmo a jellium model). Essentially the plasma frequency. Next the imaginary part is related to the relaxation time, and can be extracted from width of the Lorentzian of an electron energy loss spectrum. You can search if these datas are tabulated somewhere. Experiments to establish plasma frequency, as you say refrectivity measurements, or EELS (electron energy loss spectra). You can have a look to the chapter 5 of Andrea Marini PhD thesis.

Best,
Daniele

[Stephan]

Dear Daniele,
thank you for your reply. I think I understand now how the complex Plasma frequnecy is defined. Please tell me if I'm wrong. It is simply the eta in equation 5.6 in Andrea Marinis PhD-thesis (or is it plank constant times eta or plasma-frequency times eta).
If I'm right I whant to mention that the term "imaginary part of the Drude Frequency" is rather confusing, because that's not exactly what it is. I think one should rather call it "full width at half maximum (FWHM) of the plasmon peak in the energy-loss spectrum" or simply damping factor. These are terms one can find in literature and experimental data. I think "Complex Plasma Frequency" isn't really known in literature at least not in experimental literature.

Thanks and Regards
Stephan Ludwig
1st physical intitute
University Stuttgart

[Stephan]

Sorry, of course I just suppose that the eta is the imaginary part of the complex plasma frequency.
I suppoae the normal Plasma frequency is the real part...

Regards,
Stephan

[Daniele Varsano]

Dear Stephan,
Yes, that's right.
And I agree with you that "damping factor" would be more appropriate and easy to understand. We will take into account for the documentation of the next release.
Best,
Daniele

[Stephan]

Hello,
I have a further question concerning the Drude frequency. Is it possible to give more than one Drude-Mode as input.
Many systems are approximated with more than one Drude-modes (for example BaFe2As2 with a broad and a narrow Drude)

Thanks and regards
Stephan

[Daniele Varsano]

Dear Stephan,
no at the moment the Drude formula is implemented with one frequency only.
Best,
Daniele

[Fadil]

Dear all,

RPA for metals with finite-q calculations gives the dielectric functions with interband and intraband transitions.
I want to separate the interband and intraband transitions.
Is it possible to extract the dielectric function only with intraband transitions for finite-q calculations?

Best,
Fadıl

[Daniele Varsano]

Dear Fadıl,
unfortunately, I do not think there is a straightforward way to separate intra and inter-bands contribution and you should hard code it in the source.
Best,
Daniele

[Fadil]

Dear Daniele,

Thank you for the quick response.
I understand. Maybe I can restrict the transitions with 'EhEngyXd' tag.
How can we arrange the parameters here?
In the web site it is defined by 'Meaning: Electron-hole energy range'.
I think I should put allowed e-h energies?
How should be the signs compare to the Fermi level? Is it positive for the e and h?

Best,
Fadıl