Molecular Dynamics Simulation of Sonoluminescence: Modeling, Algorithms and Simulation Results

Sonoluminescence is the phenomena of light emission from a collapsing gas bubble in a liquid. Theoretical explanations of this extreme energy focusing are controversial and difficult to validate experimentally. We propose to use molecular dynamics simulations of the collapsing gas bubble to clarify the energy focusing mechanism, and provide insight into the mechanism of light emission. In this paper, we model the interior of a collapsing noble gas bubble as a hard sphere gas driven by a spherical piston boundary moving according to the Rayleigh-Plesset equation. We also include a simple treatment of ionization effects in the gas at high temperatures. By using fast, tree-based algorithms, we can exactly follow the dynamics of million particle systems during the collapse. Our results clearly show strong energy focusing within the bubble, including the formation of shocks, strong ionization, and temperatures in the range of 50,000---500,000 degrees Kelvin. Our calculations show that the gas-liquid boundary interaction has a strong effect on the internal gas dynamics. We also estimate the duration of the light pulse from our model, which predicts that it scales linearly with the ambient bubble radius. As the number of particles in a physical sonoluminescing bubble is within the foreseeable capability of molecular dynamics simulations we also propose that fine scale sonoluminescence experiments can be viewed as excellent test problems for advancing the art of molecular dynamics.