J. Phys. I France
Volume 6, Numéro 1, January 1996
Page(s) 149 - 166
DOI: 10.1051/jp1:1996134
J. Phys. I France 6 (1996) 149-166

A Molecular Dynamics Simulation of the Orientationaly Disordered Phase of Potassium Perchlorate

F. Affouard and Ph. Depondt

Département de Recherches Physiques URA CNRS 71, Université Pierre et Marie Curie, 4, place Jussieu, 75252 Paris Cedex 05 France

(Received 13 July 1995, accepted in final form 21 September 1995)

The orientationaly disordered phase of a relatively large system of potassium perchlorate is simulated on a massively parallel computer with strict SIMD architecture. Crystallographic results are compared with known diffraction data. Correlation densities of orientational and translational variables are computed showing orientation-translation coupling of the perchlorate ions, and coupling between a perchlorate orientation and the translation of neighbouring potassium and perchlorate ions. The orientation-orientation correlation between neighbouring perchlorate ions shows antiferromagnetic pseudo-spin type coupling corresponding to ions in opposite $T_{\rm d}$ orientations. This correlation has a lifetime which is longer than the single molecule orientational lifetime, evidence of correlated orientational motion.

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