Quantum-mechanical calculation of elastic forces in rare gas crystals

The energy of a crystal whose atoms are displaced from the lattice sites is calculated. No restrictions are imposed on the displacement vectors, provided they are small in comparison with the lattice constant. In particular, the atomic configuration may correspond to short-wave lattice oscillations. An essentially anharmonic dependence of elastic energy on displacement is obtained. The energy of interatomic pair interaction is extracted from the elastic energy, and the contribution of residual many-body interactions is estimated. The calculated sound velocity is compared with experimental data.

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