  By use of the recurrent relation approach (RRA) we study the microscopic
dynamics of liquid aluminium at T=973 K and develop a theoretical model which
satisfies all the corresponding sum rules. The investigation covers the
inelastic features as well as the crossover of our theory into the
hydrodynamical and the free-particle regimes. A comparison between our
theoretical results with those following from a generalized hydrodynamical
approach is also presented. In addition to this we report the results of our
molecular dynamics simulations for liquid aluminium, which are also discussed
and compared to experimental data. The received results reveal that (i) the
microscopical dynamics of density fluctuations is defined mainly by the first
four even frequency moments of the dynamic structure factor, and (ii) the
inherent relation of the high-frequency collective excitations observed in
experimental spectra of dynamic structure factor $S(k,\omega)$ with the two-,
three- and four-particle correlations.
