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This research has mainly concerned the microscopic dynamics of liquid alkali metals at their melting points. We have examined such dynamics applying the memory function formalism and mode-coupling theories, the theoretical results have been compared with experimental and molecular dynamics findings. Moreover, a comprehensive simulation study of the structural and dynamical properties of liquid Na, K, Rb and Cs revealed a scaling behaviour for such alkalis at the melting point. In particular, for liquid Cs the molecular dynamics results are found to be in excellent agreement with recent neutron scattering results. Finally, the analysis is extended to transport coefficients (namely, diffusion and shear-viscosity) revealing a good agreement with experimental data and confirming the validity of a simplified mode-coupling approach recently proposed (see Refs. [6,8,10]).
The more recent works have been devoted to a detailed analysis of self-properties of liquid Na and Li in a quite large interval of temperatures ranging from the melting point to the boiling point. At low temperature the main relaxation mechanism is related to the "cage effect", increasing the temperature the relaxation is dominated by the appearence of vortices in the liquid. The two different mechanisms of relaxation are related to different behaviour of the incoherent dynamical structure factors for small wavevector. These features can be explained within a simplified mode-coupling approach. An overall good agreement has been found between molecular dynamics results and neutron incoherent inelastic scattering data (see Refs. [12,19,20,25,26]).
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We have clarified the microscopic origin of fast sound in liquid water (an effect revealed by neutron scattering analysis), this effect is found to be a rather extreme case of a well-known phenomenon (namely, the positive dispersion) occuring even in monoatomic liquids. An extensive computer simulation study of water, modelled with the so-called TIP4P potential, provided a detailed account of the dispersion curve associated to longitudinal modes. These data support the results of a microscopic approach (namely, an extension of viscoelastic theory to molecular systems) that we have previously obtained. Finally, a deeper memory function analysis have shown that a combined kinetic and mode-coupling framework can qualitatively account for the basic dynamical features of the phenomenon (see Refs. [11,13,15,18]).
Finally, the study has been extended to the self properties of the structure dynamical factors (adopting a SPCE-potential to model liquid water) and the simulation results have been succesfully compared with new data of quasi elastic neutron scattering (see Ref. [24]).
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We have adopted a realistic potential for liquid water, namely the TIP4P model, to perform computer simulations in the supercooled region, at densities well below the coexistence curve. To investigate the existence of possible inhomogeneities in the simulated systems, we have estimated the associated Voronoi polyhedra distributions. Revealing, for such potential model a limit of mechanical stability at densities ~ 80 % lower than the coexistence one. The principal aim of the work was to analyze density and temperature dependence of the self diffusion coefficient D. We have shown that the temperature dependence of D in real system is well reproduced (at temperature below 277 K). Moreover, the density behaviour of D does not exhibit any relevant variation at decreasing densities, in contrast with previous simulations, performed adopting a different potential (ST2), which have revealed a dramatic decrease of D with density. These differences suggest that the effect observed in the ST2 model has to be considered peculiar of such model (see Refs. [14,16]).
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