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Chemistry LibreTexts

Kinematical theory

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. The purpose of the dynamical theory is to take this interaction into  account .