[Pw_forum] double delta

[Eyvaz Isaev]

Dear Aritz,

Please have a look at the next definitions:

1) \gamma_{qj} = 2\pi\omega_{qj}
\sum_{k,n,n'}{|g_{k+q,n';kn}^{qj}|^2 \delta
(e_{nk}-e_F)\delta (e_{n'`,k+q}-e_F)

This is so called the phonon linewidth which relates
two electrons  with different wave vectros (k, and
k+q) at the Fermi surface.
|g|^2 is the square of the electron-phonon matrix
element. 

2) \lambda_{nq} = \gamma_{nq}/(\pi N(e_F)
\omega_{nq}^2)

I.e. \gamma_{nq} which contains a production of two
\delta - functions is among main ingridients of the
electron phonon coupling constant \lambda.

 
Bests,
Eyvaz.
P.S. My apologies for the previous mail which was sent
accidently. 

--- Aritz Leonardo <swblelia at sw.ehu.es> wrote:

> Hello
> 
> could anyone tell me what is exactly de meaning of
> the double_delta in 
> e-ph calculation?
> 
> thanks!
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