Generalized collective modes in a binary He_{0.65}-Ne_{0.35} mixture

We have applied the parameter-free collective modes approach to investigate the collective excitation spectra of a He${}_{0.65}$-Ne${}_{0.35}$ gas mixture at 39.3 K. The static and dynamic correlation functions were calculated directly in molecular dynamics simulations of an ensemble of 864 particles which interact via Aziz potentials. We have compared the spectra calculated within the (basic) hydrodynamic and various extended basis sets of dynamical variables and with results obtained directly from the computer simulation. Within this formalism we were able to obtain “fast sound” type modes using an extended hydrodynamic set of seven dynamical variables. A detailed analysis of the contributions of the different spectra of collective modes to the partial dynamical structure factors showed that these “fast sound” type excitations appear due to the dynamics of the lighter He particles in the mixture.