Molecular dynamics of the phase transition in solid deuterated methane

• Published in: Australian journal of physics 1993, Vol.46 (4), p.523-533
• Main Authors: KANSAL, M. K, TRIKHA, S. K
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Physics
• ISSN: 0004-9506; 1446-5582
• DOI: 10.1071/PH930523

The rotational dynamics of a single deuterated methane molecule in the presence of its twelve nearest neighbours has been studied by using a computer simulation technique. The three-dimensional motion of the tetrahedral molecule is described by the appropriate algorithm equations, as well as by the well known Lennard-Jones potential. The importance of the inverse-twelfth-power repulsive potential for the dynamics of the deuterated methane molecule is also highlighted. The second-nearest neighbour interactions contribute only 7% to the potential energy of the whole system and this hardly affects the dynamics of the central molecule. A detailed analysis of the direction cosine data reveals a change in the dynamical behaviour of the molecule around the transition temperature, which could be attributed to the singularity observed in the specific heat data. Corresponding to the Lennard-Jones potential, the period of oscillation of the central molecule comes out to be 0 38xlO-12 s. Making use of the (dimensionless) average rotational kinetic energy at the transition, (ERK)critical = 6 3, and the period, the transition temperature is found to be 27 7 K, which is in quite good agreement with one of the ..\-type transition temperatures reported by Clusius et al.