Theory section on Documentation

[huebener]

Hello,

I noticed a small discrepancy between the Documentation page http://epw.org.uk/Documentation/Electron-phononCoupling and the paper Noffsinger et al. (http://dx.doi.org/10.1016/j.cpc.2010.08.027) which are otherwise identical. Specifically, on the website there is the distinction between the e-ph matrix elements g^SE and g, while in the paper only g is used. While, I see that the definition of g^SE is used frequently in the literature, there seems to be a contradiction between these two documents (I also note that F. Gustino http://arxiv.org/abs/1603.06965 does not seem to use this definition).

Maybe there is a subtle point that I am missing here?

Thank you very much for your help.

Cheers,
Hannes

[carla.verdi]

Hi Hannes

Indeed in the (journal) literature the prefactor is sometimes omitted, and g defined just through the braket. I think it's just an inaccuracy in the case of Noffsinger et al.; see for example the theoretical paper http://journals.aps.org/prb/pdf/10.1103 ... .76.165108 where the definitions are consistent with the ones on the website. Also, if you look at Eq.(38) of F. Gustino http://arxiv.org/abs/1603.06965 where g is defined, and then at Eq.(34) and Eq.(21), you can see that the prefactor should be included.

Cheers
Carla

[huebener]

Hi Carla,

Thank you very much. I guess this is a convention, that only leads to confusion when one is actually looking at the quantities inside the code, where the dV potentials are treated separately from the prefactors.

Much clearer now.

Cheers,
Hannes