ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
An extensive molecular dynamics study has been made as a prediction of possible structural phase changes in cyclohexane-d12, using highly parallel computers. Clusters of 128 molecules and larger are simulated, giving results for zero-pressure conditions. Intermolecular interaction is modelled by 6-exp atom-atom potentials relating all non-bonded C and D atoms of rigid chair-form molecules. The system forms the natural low-temperature structure (phase II, space group C2/c), and on heating a transition is observed at 65 ± 10 K to a new rhombohedral phase (space group R{\bar 3}m). This phase has not been found experimentally, but there is a natural unidentified metastable phase at ambient pressure and another unidentified phase under pressure. This new simulated phase persists to a further transition at 175 ± 15 K, above which there is no apparent molecular orientational ordering and the structure agrees well with the known f.c.c. plastic crystalline phase I. At 200 ± 15 K the plastic phase melts, and the liquid drop does not sublime, again in agreement with experiment. The analysis for the ordering in the clusters is done with the aid of equal area orientational and translational 'dot plots', radial distribution functions and powder diffraction patterns. Future bulk molecular dynamics simulations are suggested as a function of pressure, with the possible inclusion of the internal molecular distortion potential function.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0108767390008777
Permalink
