1. Solving the problem of crystal structure

The fundamentals of geometrical crystallography and X-ray diffraction of crystals are described in [1, 2, 3] . The article [4] in Techniques de l'Ingénieur describes the theory of crystal structure determination by X-ray diffraction. In particular, it has been shown that this determination involves tracing the crystal's electron density map, since X-rays interact with electrons. In a way, they can be said to count them: this makes it possible to relate the height of an electron density peak to the number of electrons in an atom, and thus to chemically identify the nature of the atom located at a point with coordinates x,y,z.

Calculation of the electron density ρ ( x, y, z) at any point with coordinates x,y,z, taken in arbitrary units...