Microscopic theory of orientational disorder and the orientational phase transition in solidC60

We have developed a microscopic theory which describes the orientational dynamics of ${\mathrm{C}}_{60}$ molecules in the face-centered-cubic phase of ${\mathrm{C}}_{60}$ fullerite. The molecular interaction potential and the crystal-field potential are formulated in terms of symmetry-adapted rotator functions. The phase transition to the Pα3¯ structure is driven by an active multipolar of ${\mathit{T}}_{2\mathit{g}}$ symmetry belonging to the l=10 manifold. The Birman criterion is satisfied. The transition is found to be of first order.