Lattice dynamics of ortho-terphenyl

A lattice dynamical calculation for the known crystal structure of orthoterphenyl has been carried out under the rigid molecule approximation. The optimized parameters for the intermolecular potential reproduce adequately both the equilibrium crystal structure as well as the experimental heat capacity up to 35 K. The values for the mean-square-displacement as calculated from the computed vibrational density of states show that for temperatures well above 50 K most of the motions contributing to the atomic displacements as measured by neutron quasielastic scattering arise from the thermally excited internal molecular modes. The implications for the recent tests of kinetic theory predictions regarding the liquid-glass transitions using this material are briefly discussed.