Lattice Dynamics of the Orientationally Ordered Crystal C₆₀

Abstract

A calculation of the vibrational spectrum of intermolecular modes of the low-temperature orientationally ordered crystalline phase of fullerene C,, is carried out in the approximation of an intermolecular potential which includes two contributions: the atom-atom Lennard-Jones (12-6) potential and a noncentral interaction. This model has allowed to approximate satisfactorily the experimental data on neutron scattering, temperature dependence of specific heat, and bulk modulus. Phonon dispersions, sound velocities, elastic constants, and densities of vibrational states are calculated. It is shown that in the centre of the Brillouin zone librational modes which are Raman active should be located in the region 20 to 30cm-' and infrared active translational modes should be in the range 40 to 60 cm-I.