Revisiting the energy treatment of the density of molecular crystals: an interrelation between intermolecular interaction energies and changes of molecular volume

An interrelation between the density and lattice energy of molecular crystals is analyzed based on the results of quantum chemical calculations of model supramolecular associates. Using the Interacting Quantum Atoms approach and calculations of molecular volume changes upon the onset of intermolecular interactions, it was found that the deformation energy (a contribution to the lattice energy) depends on the “densification” of a molecule. The significance of these dependences under variation of the electron density isosurface used for molecular volume calculations is studied. An important role is demonstrated of the choice of the isosurface for consistent description of intermolecular interactions using the geometric approach based on the volume and density and the energy treatment based on the lattice energy.