Instantaneous Normal Modes of Yukawa Liquids

ABSTRACT The instantaneous normal mode (INM) approach, which extends the normal mode description of collective excitations in solids to liquids, is applied to strongly coupled, three‐dimensional Yukawa liquids. Based on data from Langevin dynamics simulations, we compute the instantaneous normal modes across a wide range of coupling and screening parameters. Yukawa liquids at weak to moderate screening exhibit a pronounced maximum in the INM density of states, which disappears as the coupling decreases or screening becomes stronger. The fraction of unstable modes displays a quasi‐universal behavior, which can be described to a large extent by an effective coupling strength. The relation of the INM approach to the quasi‐localized charge approximation (QLCA) is explored in some detail. In particular, the QLCA dispersion relation can be recovered explicitly from an appropriately weighted mode spectrum.