Abstract:
Collective motions of atoms in molecular dynamics model of classical Lennard-Jones
crystal are under consideration in process of heating up to spinodal decomposition and
subsequent cooling of the melt to spontaneous crystallization. Collective motions magnitude hysteresis was found. A new numerical method based on four-point correlator usage
was used for studying collectivity in the motion of atoms in crystals. This correlator
represents the mean cosine of angle between replacement vectors of two atoms over time $\tau$, which were initially close to each other. Two features were found: (a) correlator increases with temperature in monocrystal; (b) correlator in polycrystal, which was formed
during crystallization, appeared to be higher than in initial monocrystal. Distributions of
correlator's values over the angles between displacements were computed. Two contributions in atoms’ motions were distinguished: first is anisotropic, temperature independent
and second is almost isotropic, which angular distribution has the form of the Boltzmann
distribution. Excitation energies, which corresponds to second contribution, were calculated.