The coupling of the thermal motions of the atoms in a crystal as deduced from the acoustic spectrum of the thermal diffuse scattering

The strength of the coupling of the motions of the atoms in different cells of a crystal is investigated by means of the acoustic spectrum of the thermal diffuse scattering. The calculations are performed for a monatomic cubic crystal. Correlation coefficients, which express the amount of in-phase motions of remote atoms in the crystal, are approximately determined from the term of the acoustic spectrum. This term is valid for all crystals. We find that the coupling of the motions of the atoms is approximately inversely proportional to the distance between the atoms in the crystal.