In the 1930s Brillouin and Born suggested that a crystal's shear moduli decreases with temperature and that the crystal melts when at least one of the shear moduli reaches zero. As far as I can see, the theory is still controversial with different experimental and computational studies reaching divergent conclusions on the theory's validity. Is the theory believed to be correct for organic molecular crystals? Can you point me to relevant papers? Thanks!
Thanks Mikhail. I agree, from my own computational experience, the shear modulus is still non-zero at the melting temperature. Another thing.... In solid-solid phase transitions where one polymorph transitions into another, then some elastic constant becomes zero. When the crystal breaks symmetry, then the bulk modulus turns to zero. Doesn't this mean that as the temperature increases, the crystal will loose one symmetry after the other in succession, until it reaches P1, and only then will it melt?
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