MOLECULAR-DYNAMICS SIMULATION OF INCOMMENSURATE PHASES

The article outlines the essential information on the properties of the incommensurate phases necessary for constructing a semi-microscopic model of a real crystal, and shows how to perform a molecular-dynamics simulation of such a model. The calculated dynamical structure factor shows a soft, underdamped phonon mode above the critical temperature and in the incommensurate phase both phase and amplitude modes. The kinetic variation of the wave vector modulation of the incommensurate phase leads to a non-equilibrium devil's staircase with quasisteps at irrational numbers which are attributed to the nucleation and growth of stripples. Point defects may hinder the propagation of stripples. The stripple can be blocked at the domain wall btween two domains of tilted zig-zag incommensurate phase where it forms a kink. The basic formulae necessary to carry out the molecular-dynamics simulation of an incommensurate model are quoted.