On the absence of a positive sound dispersion in the THz dynamics of glycerol: an inelastic x-ray scattering study

Collective dynamics in binary liquids: a molecular dynamics study of the composition dependence of the spectra of collective excitations

The spectra of longitudinal and transverse collective excitations in liquid binary metallic Na(c)K(1-c) alloys are studied for pure components and four different concentrations. A theoretical generalized collective modes approach is used to analyze the concentration dependence of the dispersion of acoustic and optic branches in a wide region of wavenumbers. The dispersion of longitudinal collective excitations in binary alloys is estimated from the eight-variable thermo-viscoelastic dynamic model with full account of thermal fluctuations. It is found that the longitudinal and transverse branches show different dependences on concentration in the short-wavelength region. The issue of 'positive dispersion' of acoustic excitations in liquid binary alloys on the boundary of the hydrodynamic regime is discussed. It is shown that the coupling between longitudinal acoustic and optic modes is responsible for an increase of the 'positive dispersion' close to equimolar composition.

Ab initio study of collective excitations in a disparate mass molten salt

Ab initio molecular dynamics simulations and the approach of generalized collective modes are applied for calculations of spectra of longitudinal and transverse collective excitations in molten LiBr. Dispersion and damping of low- and high-frequency branches of collective excitations as well as wave-number dependent relaxing modes were calculated. The main mode contributions to partial, total, and concentration dynamic structure factors were estimated in a wide region of wave numbers. A role of polarization effects is discussed from comparison of mode contributions to concentration dynamic structure factors calculated for molten LiBr from ab initio and classical rigid ion simulations.