Towards a realistic model for the quantitative evaluation of intermolecular potentials and for the rationalization of organic crystal structures. Part II. Crystal energy landscapes

Abstract

Many crystal structures were generated by a computer predictor for naphthalene, naphthoquinone, 1,2-dichlorobenzene, 2,3-dimethylbenzoic acid, parabanic acid and pyridine, and the lattice energies were then calculated by standard atom–atom potentials, by point-charge models, and by the SCDS-Pixel method. Using results from the latter approach, the relative importance of coulombic, polarization, dispersion and repulsion energies in crystals is discussed in relationship with the chemical characteristics of the constituent molecule, with crystal density, and with some key crystal structural factors like interplanar angles and some intermolecular distances believed to be indicators of crystal stabilization. In general, intermolecular interactions are better discussed when considering the electron density of large molecular moieties or of entire molecules, than when considering atom–atom distances. Significant comparisons between atom–atom energies and the more accurate Pixel energies are presented. The performance of the Pixel-SCDS method in ranking crystal energies against experimental structures, in the so-called crystal structure prediction exercise, is comparable to, and sometimes better than that of atom–atom force fields.