Structure and lattice dynamics of the ordered phase of solid CT0

Harmonic lattice dynamics calculations have been performed on the low temperature structure of solid CT,,. The theoretically obtained lattice structure agrees with the experimentally determined low temperature structure and the symmetry is found to be P2,/m. The orientationally ordered equilibrium is obtained by using van der Waals interactions only, i.e. without including Coulomb interactions. The calculations yield additional information on the orientational ordering. The calculated frequencies of the 12 Raman active lattice modes agree quantitatively with the recently observed Raman spectrum. The frequencies of the nine complementary IR active lattice modes are predicted. 1