I am running calculations using the BSE for core-level spectroscopy, and turned on the dfoffdiag="true" flag in <xs> in order to have access to the entire dielectric tensor.
Could someone please tell me where the geometrical information about the component 1,2, and 3 of the tensor are written?
In particular if the unit cell has non-orthogonal basis vectors, what is the convention ? Is 1 along x, 2 in the xy plane and 3 completes a right -handed frame?
Sorry in advance if I have missed this info.