Two-step rotational relaxation in glassy crystal cyanoadamantane

Results of molecular-dynamics numerical simulations are presented for a simple model of glass forming orientationally disordered crystal. In this system, glass formation is not induced by quenched diluted disorder, but it occurs similarly to conventional glasses. Simulations show that the relaxational dynamics of this orientational glass involves a multiple-step mechanism. The simplicity of the system and the existence of an underlying average lattice allows us to visualize clearly the molecular motions involved in the different relaxational processes. The role of translation-rotation coupling is stressed. The results obtained with this model are used to discuss the validity and occurrence of the mode coupling theory in the experimental system. [S0163-1829(99)50614-0].