Clarify the choice of Q₀

[kavanase]

Flagged by discussions with @kantaimperial; the logic behind the choice of Q₀ in the examples is not really clear.

From our discussions before @xw-w, this should correspond to the central datapoint used for e-ph coupling right? Can we make this clear with a comment/note in the example tutorial?

Also, in the example case given in the notebook, disp_004 is used in both cases for hole and electron capture e-ph coupling (as we usually do the two together), but then different Q₀ values (0.4*delQ and 1.4*delQ) are used? Is this correct or a typo?

[xw-w]

Thanks for pointing it out and I've corrected the typo. The choice of Q₀ is not unique as long as it meets the criterion I noted in the tutorial (i.e. a single-particle defect level should be well defined and be in the bulk band gap) and you may want to do your own tests for your system

[kavanase]

Yes but in the notebook it's not obvious to most people that the configuration chosen for e-ph coupling (disp_004 in this case) is the same as Q₀, so I think this should be clearly stated

[xw-w]

Sorry but I thought I wrote in the notebook that "The reference WAVECAR used for WSWQ calculations corresponds to {Q_0}. "? Please feel free to edit the example if you think anywhere is not clear! :)