Inelastic X-ray Scattering Study of the Collective Dynamics in Simple Liquid Metals

The collective dynamics of the so-called `simple' liquids (in particular,
liquid metals) are a good paradigm to illustrate the capabilities of
inelastic X-ray scattering (IXS). In particular, it is shown how the
present accuracy of the data can be exploited to provide not only a
precise determination of the main spectral features (dispersion
relations), but also a clue for the physical assessment of the microscopic
relaxation mechanisms underlying the dynamics of the liquid state.
Starting from new IXS data on liquid sodium as an example, we apply a
generalized hydrodynamic framework in order to describe the details of the
experimental lineshapes. A comparison with recent data on liquid lithium
and aluminium is also reported: although quantitative differences indicate
that the principle of corresponding states seems not to be applicable, in
all these systems a simple viscoelastic approach turns out to be
inadequate to reproduce the experimental data.