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This study defines the Frenkel line for Yukawa fluids, identifying the dynamic crossover condition where the roton minimum in the dispersion relation of longitudinal excitations emerges. Utilizing self-consistent relaxation theory, the authors determine thermodynamic states where this roton minimum vanishes, aligning their findings with molecular dynamics simulations of the Yukawa fluid's phase diagram. The research reveals that the Frenkel line can be directly inferred from the static structure factor, providing a new perspective on the vibrational dynamics of simple liquids near this critical line.
The Frenkel line can be pinpointed from structural characteristics, revealing a direct link between vibrational dynamics and phase behavior in Yukawa fluids.
For a simple model fluid, the Yukawa fluid, the condition for dynamic crossover, known as the Frenkel line, is defined. The condition is related to the fact that the roton minimum in the dispersion relation of longitudinal acoustic-like excitations exists only when the collective vibrational dynamics of particles dominates in the liquid. Based on the self-consistent relaxation theory for the Yukawa fluid, thermodynamic states are determined in which the roton minimum disappears. The obtained values of the state parameters for the Frenkel line are consistent with the results of studies in which the position of this line on the phase diagram of the Yukawa fluid was determined using molecular dynamics simulations. It is shown that the Frenkel line in this system can be determined directly from the structural characteristic - the static structure factor. A physical interpretation of the roton minimum frequency for simple liquids near the Frenkel line is proposed.