Grenzen der Kristallstrukturbestimmung: Elektronendichte und chemische Bindung

Abstract

The experimental determination of electron distributions in crystals is based on models and assumptions whose implications should be remembered during the evaluation of the results. Thus, the crystallographic phase problem is solved on the basis of the standard procrystal model, and it is assumed that the deficiencies of the kinematical diffraction theory can be corrected for. Generalizations of the procrystal model using multipolar functions offer important advantages. The qualitative interpretation of the results and the concomitant development of quantum mechanical calculations continue to be the most fruitful field of application. The concept of atomic charge is very useful but also qualitative since the definition of atomic fragments is ambiguous. Of all the physical properties of the crystal structure, the electrostatic potential and its derivatives are most easily computed, but even these calculations require additional assumptions.