Collective excitations in Hydrogen across the pressure-induced transition from molecular to atomic fluid

I. -M. Ilenkov; T. Bryk

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arXiv · 2506.20791

Collective excitations in Hydrogen across the pressure-induced transition from molecular to atomic fluid

I. -M. Ilenkov·T. Bryk

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Abstract

Dispersion of collective excitations in fluid Hydrogen along the isothermal line T=2500~K, including the region of molecular-to-atomis fluid transition, is studied by ab initio molecular dynamics (AIMD) simulations. The obtained density dependence of the adiabatic and high-frequency speed of sound contains a plateau in the region of the molecular-to-atomic fluid transition. We show, that the five-variable thermo-viscoelastic model of generalized hydrodynamics for pure molecular H$_2$ and pure atomic (H) fluids is able to recover perfectly the AIMD-derived time correlation functions and sound eigenvalues nicely agree with the numerically estimated sound dispersion. In the region of the molecular-to-atomic fluid transition a dynamic model of chemical reacting mixture should be applied. We discuss the calculations of time correlation functions from molecular/atomic units in the reacting mixture from AIMD trajectories.

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I. -M. Ilenkov, T. Bryk. 2025-06-25. Collective excitations in Hydrogen across the pressure-induced transition from molecular to atomic fluid. https://arxiv.org/abs/2506.20791

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