WAVEDER

The file WAVEDER contains the derivative of the orbitals with respect to k, more precisely the matrix

$\langle \phi_{n'k} |{\bf S} | \frac{\partial \phi_{nk}}{\partial k_i}\rangle = \frac{1}{\epsilon_{nk} -\epsilon_{n'k}} \langle \phi_{n'k} | \frac{\partial (\mathbf{ H} - \epsilon_{nk} \mathbf{S})}{\partial k_i} | \phi_{nk} \rangle.$

These matrix elements also correspond to the dipole moment between the states $\phi_{n'k}$ and $\phi_{nk}$, 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.

Related Tags and Sections

GW calculations

BSE calculations

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