Polarization average for BSE spectra

[palful]

It would be nice to add the explicit option to get_chi in YamboExcitonDB in order plot polarization-averaged BSE spectra, by adding a function that calls exciton_dipoles and then get 1/3 \sum_i eps_ii(w) (i=x,y,z) if needed by the user.

[sangallidavide]

Also to have the off-diagonal elements of the dielectric tensor ;-)

[palful]

Can we actually get the full tensor with a standard BSE calculation? Maybe the function polarization_mode by Riccardo goes in that direction if it's a matter of rotating the polarization

[sangallidavide]

Can we actually get the full tensor with a standard BSE calculation? Maybe the function polarization_mode by Riccardo goes in that direction if it's a matter of rotating the polarization

Sure. Yambo already computes the off diagonal elements for the kerr effect.
By changing what you use for the dipoles, (<x>, <sigma>, <m_orb>, etc ... ) you can even get more