Molecular-dynamics study of ferrodistortive phase transitions

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Abstract
Molecular-dynamics results simulating a canonical ensemble are presented and discussed for a two-dimensional one-component displacement model for ferrodistortive structural phase transitions. Our results include: I) There is strong evidence that the system undergoes a continuous phase transition, except at the displacive limit. 2) For three different sets of model parameters, the static critical exponents are found to be model parameters independent and consistent with those of the two-dimensional Ising model. 3) The formation of clusters of locally ordered regions is demonstrated. 4) Close to Tc and at the wave vector kc, where the order-parameter susceptibility diverges, we observe a central peak around ω = 0 in the dynamic form factor of the density fluctuations. 5) For wave vectors slightly away from kc the central peak splits into a double-peak structure, giving rise to a new excitation branch. 6) The central peak and the new excitation branch are traced back to travelling cluster waves and their lifetime. 7) The cluster dynamics is shown to dominate the critical slowing-down.