AbstractAccording to the Hohenberg‐Kohn‐theorem the valence electron density (VED) determines the electronic ground state of crystal. The VED can be constructed measuring the X‐ray scattering amplitudes. Parametric density models are developed in order to complete the experimental data and to enable a generalization of the solved structure parameters. Caused by experimental and methodic errors various density models are able to describe the experimental data with comparable accuracy. However, electrostatic criterions can be applied in order to select a density model, which describes also the dynamical structure–property connections of semiconductor. A quantitative calculation of internal forces is possible by use of the generalized Berlin‐Theorem. The electrostatic model contains the ion–ion‐ and the electron–ion interaction in the crystal. The latter one can be calculated in the Fourier space using experimental or theoretical structure amplitudes. A model is proposed specially designed for diamond and zincblende structure compounds. The elastic properties of covalently bonded materials are described sufficiently precise by a bond charge model, taking into account the variation of amount and extension of the bond charge by deformation of lattice. The so fitted VED response of binary compounds can be transfered to solid solutions in order to interprete quantitatively the measured internal deformations in such materials.