Drude parameters requirement (metal)

[muhammadhasan]

Hi,

I have a question regarding the dielectric function calculation for metals. In Yambo, when we calculate the dielectric function at q → 0, we use Drude parameters to account for intraband transitions. However, at finite q values (q ≠ 0), the Drude parameters are not used—yet all intraband transitions are still taken into account.
Could you please explain why Yambo requires Drude parameters at q = 0, but not at finite q?

Best regards
Md J Hasan
Graduate student, Mechanical Engineering
University of Maine

[Daniele Varsano]

Dear Md J Hasan,

at finite q the intraband contributions are taken into account numerically as they involve transitions between occupied and unoccupied states located at different k points (k-k'=q).
In the limit q-->0 instead, this operation cannot be done numerically in a straightforward way.

We have recently developed a scheme to calculate the limit q->0 without resorting to the Drude model, this will be published and made available in the next futre.

Best,

Daniele