Measurements of electron densities in solids: a real-space view of electronic structure and bonding in inorganic crystals

This review summarizes the recent progress in experimental determination of electron densities in inorganic crystals and its contribution to our understanding of bonding and density functional approximations. The experimental techniques for electron density mapping are presented, including the accurate measurement of experimental structure factors by electron diffraction and multipole electron density modelling. Interpretation of electron density maps by combining first-principles calculations and spectroscopic measurements will be illustrated through the example of bonding in copper and cuprite. The significance of experimental electron density is demonstrated by selected examples of materials representative of ionic, metallic and covalent bonding and testing of theory.