Analysis of translation-rotation coupling in an orientationally disordered ionic crystal

Molecular dynamics calculations are used to study the coupling between translations and rotations in a model appropriate to solid sodium cyanide in its orientationally disordered high temperature cubic phase. Static properties are analysed via the formalism of Michel and Naudts through the introduction of a wavevector dependent parameter λ which measures the extent of translation-rotation coupling. The dynamics of the crystal are shown to be described accurately by a Mori-type theory, similar to that adopted by de Raedt and Michel, in which collective time correlation functions are expressed in terms of λ and certain other static averages. The same approach is used to discuss the crystal dynamics in the region of long wave-length, where the molecular dynamics calculations yield no direct information.

[1]  I. R. Mcdonald,et al.  Static disorder in the mixed crystals (KCN) x (KBr)1−x and its relation to dynamical properties , 1982 .

[2]  S. Mahanti,et al.  Theory of elastic and phonon softening in ionic molecular solids. Application to alkali cyanides , 1982 .

[3]  I. R. Mcdonald,et al.  The rotator phase of solid caesium cyanide , 1982 .

[4]  S. Mahanti,et al.  Elastic Softening and Ferroelastic Instabilities in Alkali Cyanides and Superoxides , 1982 .

[5]  I. R. Mcdonald,et al.  Molecular-dynamics study of phase I of RbCN , 1981 .

[6]  I. R. Mcdonald,et al.  Anisotropy of the Electrostatic Interactions and the Properties of Orientationally Disordered Cyanide Crystals , 1981 .

[7]  K. R. Jeffrey,et al.  NMR investigation of orientationally disordered NaCN and KCN , 1981 .

[8]  M. Klein,et al.  Coupling of rotations and translations in cyanide crystals , 1981 .

[9]  D. Fontaine,et al.  Etude des spectres de diffusion Raman des cyanures de sodium et de potassium en phase plastique , 1979 .

[10]  N. Hush,et al.  Finite-field method calculations. IV. Higher-order moments, dipole moment gradients, polarisability gradients and field-induced shifts in molecular properties: Application to N2, CO, CN−, HCN and HNC , 1978 .

[11]  S. Haussühl,et al.  Cubic sodium cyanide, another crystal with KCN‐type anomalous thermoelastic behaviour , 1977 .

[12]  J. Naudts,et al.  Anomalous thermoelastic behavior and molecular reorientations in crystals , 1977 .

[13]  Antoinette J. Taylor,et al.  Thermodynamic and structural properties of liquids modelled by ‘2-Lennard-Jones centres’ pair potentials , 1977 .

[14]  J. M. Rowe,et al.  Crystal dynamics of KCN and NaCN in the disordered cubic phase , 1975 .

[15]  G. Pawley,et al.  On the lattice dynamics of solid nitrogen , 1974 .

[16]  G. Shirane,et al.  Dynamical critical phenomena in ND4Br , 1974 .

[17]  S. Haussühl.  Anomalous thermoelastic behaviour of cubic potassium cyanide , 1973 .

[18]  J. M. Rowe,et al.  Single crystal neutron diffraction study of sodium cyanide , 1973 .

[19]  Donald E. Williams.  Nonbonded Potential Parameters Derived from Crystalline Hydrocarbons , 1967 .

[20]  L. Verlet.  Computer "Experiments" on Classical Fluids. I. Thermodynamical Properties of Lennard-Jones Molecules , 1967 .

[21]  H. Mori.  Transport, Collective Motion, and Brownian Motion , 1965 .

[22]  R. Zwanzig.  Ensemble Method in the Theory of Irreversibility , 1960 .

[23]  W. Przygocki.  Dynamical light scattering , 1983 .

[24]  K. Michel,et al.  Orientational relaxation in molecular solids with translation rotation coupling , 1980 .

[25]  J. Naudts,et al.  Dynamics of translations and rotations in molecular crystals , 1978 .

[26]  L. Staveley,et al.  Disorder in crystals , 1978 .

[27]  J. M. Rowe,et al.  Neutron scattering studies of crystal dynamics and order-disorder phase transitions in alkali cyanides , 1977 .

[28]  S. Haussühl,et al.  Brillouin scattering in cubic potassium cyanide , 1976 .

[29]  M. P. Tosi,et al.  Ionic sizes and born repulsive parameters in the NaCl-type alkali halides—II: The generalized Huggins-Mayer form☆ , 1964 .

[30]  M. Born,et al.  Dynamical Theory of Crystal Lattices , 1954 .