WAVEDER
The file WAVEDER contains the derivative of the orbitals with respect to k, more precisely the matrix
[math]\displaystyle{ \langle \phi_{n'k} |{\bf S} | \frac{\partial \phi_{nk}}{\partial k_i}\rangle = \frac{1}{\epsilon_{nk} -\epsilon_{n'k}} \langle \phi_{n'k} | \frac{\partial (\mathbf{ H} - \epsilon_{nk} \mathbf{S})}{\partial k_i} | \phi_{nk} \rangle. }[/math]
These matrix elements also correspond to the dipole moment between the states [math]\displaystyle{ \phi_{n'k} }[/math] and [math]\displaystyle{ \phi_{nk} }[/math], which are used in both GW and Bethe-Salpeter calculations.
In the case of degenerate states, the matrix elements are set to zero, within numerical accuracy.