Revealing the intermolecular bonds in molecular crystals through charge density methods

This chapter is essentially aimed at revealing visible features associated with intermolecular interactions, in particular in crystals. The focus is narrowed to those features that may be generically obtained through electron-density-based descriptors, though those based on the full first order density matrix or the pair density will also be mentioned occasionally, especially for the sake of comparison. The chapter briefly reviews how the electron density is reconstructed from the X-ray data; illustrates a number of electron-density-based methods able to reveal intermolecular interactions in molecular crystals, such as those applying the Quantum Theory of Atoms in Molecules, the Source Function and the Reduced Density Gradient descriptors; then discusses their application to a few selected paradigmatic cases.