Order-Disorder phase transition in molecular systems, such as structural phase transformations in molecular solids or nematic-isotropic transitions in liquid crystals, can be studied in details by means of constant pressure-constant temperature molecular dynamics computer simulation. A number of microscopically defined order parameters can be computed in order to describe the transitions within the framework of Landau theory. Simulation allows to study in details the orientational motion and the diffuse scattering observed in neutron and X-ray scattering experiments in the high temperature orientationally disordered solid phases, and to quantify the role of the translation-rotation coupling in the ordering process. Strong coupling, when present, may be held responsible for the appearance of metastable phases on cooling of the disordered system. In these cases it is possible to show that the mechanism of phase transition can be completely controlled by pre-ordering processes in the disordered phase.

ORIENTATIONAL DISORDER AND STRUCTURAL PHASE-TRANSITIONS IN PLASTIC MOLECULAR-CRYSTALS / Ferrario, Mauro. - STAMPA. - 205(1991), pp. 381-393. ((Intervento presentato al convegno NATO ADVANCED STUDY INST ON COMPUTER SIMULATION IN MATERIALS SCIENCE : INTERATOMIC POTENTIALS, SIMULATION TECHNIQUES AND APPLICATIONS tenutosi a AUSSOIS, FRANCE nel MAR 25-APR 05, 1991.

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