ROTATIONAL-DYNAMICS IN ORIENTATIONALLY DISORDERED K CLO4

A molecular dynamics simulation of a 8 x 8 x 8 cells potassium perchlo rate crystal in the orientationally disordered phase was carried out u sing a CM-5 parallel computer in order to study the individual and two -molecule rotational dynamics of the ClO4 ions. Symmetry adapted rotat or functions and the rotation matrix are used to overcome the difficul ty of dealing with orientational variables. The crystal structure is f ee, with most probable Td symmetry molecular orientations, in agreemen t with experiments. The rotational motion turns out to be diffusive, b ut molecules which are far from the most probable orientations have gr eater rotational velocity. The relative orientations of two neighborin g molecules last longer than that of a single molecule, showing couple d motion. Copyright (C) 1998 Elsevier Science B.V.