Abstract
Using concepts from the theory of quantum crystals, we propose a new description of the coupling between orientational and translational fluctuations in molecular crystals. The theory treats in a selfconsistent way the interplay between collective and local fluctuations near structural phase transitions. An increase of local fluctuations leads to a decrease of lattice mediated interactions and to a softening of the crystal field potential. As a consequence of this feedback effect, the single particle orientational probability distribution becomes more and more isotropic close to the phase transition. The theory gives a unified explanation of a number of experimental results.
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Michel, K.H. Phase transitions in strongly anharmonic and orientationally disordered crystals. Z. Physik B - Condensed Matter 54, 129–137 (1984). https://doi.org/10.1007/BF01388064
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DOI: https://doi.org/10.1007/BF01388064