# Kinematical theory

### From Online Dictionary of Crystallography

Théorie cinématique (*Fr*). Kinematische theorie (*Ge*). Teoria cinematica (*It*). 運動学的回折理論 (*Ja*). Кинематические теория (*Ru*). Teoría cinemática (*Sp*).

## Definition

In the **kinematical** or **geometrical** theory, the amplitudes diffracted by a three-dimensional periodic assembly of atoms (Laue) or by a stack of planes (Darwin) is derived by adding the amplitudes of the waves diffracted by each atom or by each plane, simply taking into account the optical path differences between them, but neglecting the interaction of the propagating waves and matter. This approximation is not compatible with the law of conservation of energy and is only valid for very small or highly imperfect crystals. This interaction is taken into account by the dynamical theory.

In the kinematical theory, the integrated intensities of the Bragg reflections are proportional to the square of the modulus of the structure factor, [math]|F_{hkl}|^2[/math]. In the dynamical theory, they are proportional to the modulus of the structure factor, [math]|F_{hkl}|[/math].