On closed-shell interactions, polar covalences, d shell holes, and direct images of orbitals: The case of cuprite

Detailed experimental evidence is presented in supporting the previous report of the authors on the direct observation of d-holes and Cu-Cu bonding in Cu₂O (see figure). It is shown that the accuracy of X-ray measurements of charge density is limited by the extinction effect, and that theoretical calculations of charge transfer are limited by the approximations made and the models used.