Abstract
Molecular dynamics results are reported concerning cooperatively rearranging regions in simulated Ni0.5Zr0.5 melts down to 700 K. Emphasis is laid on discriminating between clusters of mobile atoms (CMA) from low-frequency dynamics and the all-frequency case, where the former characterize fluctuations and relaxations on the scale of the late beta regime and alpha decay, while the latter include, in addition, reversible high-frequency vibrations. Separation of the low-frequency part of the dynamics is carried out by low-pass filtering, exploiting the separation of time scales below the critical temperature T-c of the mode-coupling theory. With increasing temperature, the low-frequency and all-frequency dynamics merge in the range of T-c when the separation of time scales disappears. In the low-frequency CMA, the average size of correlated clusters of connected atoms turns out to be nearly one order of magnitude larger than in the all-frequency CMA. The low-frequency CMA appear as local clusters propagating extremely slowly in space with characteristic time scale of mu s at 700 K, the scale of the onset of alpha decay.