Molecular recognition in organic crystals : Directed intermolecular bonds or nonlocalized bonding?

Molecules are held together mainly by forces acting between individual atoms. Does the same apply to molecular clusters? Does intermolecular cohesion depend on weak bonds between individual atoms in different molecules or on less localized, more diffuse interactions between molecules? We discuss these questions from several viewpoints and in particular compare interpretations based on the extension of Bader's atoms in molecules (AIM) theory to cover closed-shell intermolecular interactions with interpretations based on the new pixel method for the calculation of coulombic, polarization, dispersion, and repulsion energies from the electron density of molecular clusters.