Electrostatic Molecular Interaction from X-ray Diffraction Data. I. Development of the Method; Test on Pyrazine

Electrostatic interaction is often an important part of the total interaction between molecules. It depends on the electron density distribution in the participating molecules, which can, in principle, be determined by X-ray diffraction methods. A method is described to calculate the electrostatic interaction between two nonpenetrating molecules by adding the pair-wise interaction between the constituent atoms. The molecular electron density distribution is expressed in terms of the densities corresponding with spherical atoms and deformations according to Hirshfeld's method. The electrostatic interaction between the various deformation densities is replaced by the interaction between the atomic multipole moments corresponding with the deformation densities. Application of the method to pyrazine, C4H4N2, showed qualitative agreement with results based on quantum-chemical calculations.