Diffusion in liquid metals is directed by competing collective modes

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Abstract
The self-diffusion process in a dense liquid is influenced by collective particle movements. Extensive molecular dynamics simulations for liquid aluminium and rubidium evidence a crossover in the diffusion coefficient at about 1.4 times the melting temperature T m , indicating a profound change in the diffusion mechanism. The corresponding velocity autocorrelation functions demonstrate a decrease of the cage effect with a gradual set in of a power-law decay, they celebrate long time tail. This behavior is caused by a competition of density fluctuations near the melting point with vortex-type particle patterns from transverse currents in the hot fluid. The investigation of the velocity autocorrelation function evidences a gradual transition in dynamics with rising temperature. The competition between these two collective particle movements, one hindering and one enhancing the diffusion process, leads to a non-Arrhenius-type behavior of the diffusion coefficient around 1.4 T m , which signals the transition from a dense to a fluidlike liquid dynamics in the potential energy landscape picture.
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  • Centre Informatique National de l’Enseignement Supérieur (INP2227/72914/gen5054)
  • Grenoble Alpes (ANR-19-P3IA-0003)
  • Solimat (ANR-22-CE92-0079-01)

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