THE MOLECULAR ELECTRON-DENSITY DISTRIBUTION - MEETING PLACE OF X-RAY-DIFFRACTION AND QUANTUM-CHEMISTRY INTERMEDIATE BETWEEN THEORY AND EXPERIMENT

Quantum chemistry and the concepts used daily in chemistry are increasingly growing apart. Among the concepts that are able to bridge the gap between theory and experimental practice, electron density distribution has an important place. The study of this distribution has led to new developments in theory, including Hellmann-Feynman theory and the density functional theory. The possibilities and limitations of these methods are discussed. Various ways of analysing the electron density distribution are presented and discussed. X-ray diffraction enables us to "observe" the electron density distribution and electrostatic properties. Experimental results are compared with the results of quantum chemical calculations. It is shown that even intermolecular interaction is observable with this method. Problems in determining ionic charges are seen to be inherent in the method.