Molecular dynamics simulation study of cyclohexane guest molecules in the cyclohexane/thiourea inclusion compound

Molecular dynamics simulations of the cyclohexane/thiourea inclusion compou nd within the high temperature rhombohedral phase (at 173 and 273 K) are pr esented. The simulated systems consist of 96/288 cyclohexane/thiourea molec ules, corresponding to 12 contiguous host thiourea channels of approximatel y 50 Angstrom length. The atomic trajectories were obtained over 600 ps ass uming rigid molecules. The orientational distribution of cyclohexane guest molecules is described through the polar angles between the guest molecular C-3(m) symmetry axis and the thiourea host reference frame. From the molec ular dynamics simulations we obtain the three-dimensional orientational dis tribution functions P(theta, phi). It is shown that the cyclohexane guest m olecules reorient about the C-3(c) and the C-2 symmetry axes of the crystal lographic 32 site. The incoherent intermediate scattering functions have be en computed from molecular dynamics trajectories, allowing the development of theoretical models that could be used to interpret the dynamics of cyclo hexane guest molecules from experiments. (C) 2000 Elsevier Science B.V. All rights reserved.