Is there something of mode coupling theory in orientationally disordered crystals?

Molecular dynamics simulations have been performed on the orientationally disordered crystal chloroadamantane. We stress that universal behavior, relatively well described by the mode coupling theory, is shared by systems whose dynamics are almost completely controlled by translations or rotations. This investigation also shows the existence of a second remarkable dynamical crossover at the temperature Tx>Tc, consistent with a previous NMR and molecular dynamics study [F. Affouard et al., Europhys. Lett. 53, 611 (2001)]. This allows us to support clearly the existence of a "landscape-influenced" regime as recently proposed [S. Sastry et al., Nature 393, 554 (1998)].