FROM MACROSCOPIC TO ATOMIC MOTIONS IN LIQUID-METALS

In the present review of liquid dynamics studies on liquid metals are reported. Particularly the case of liquid lead is reviewed because this case was carefully studied by neutron scattering technique, S(Q,ω) being determined at two widely different temperatures T=623 K and T=1170 K and therefore different densities. In addition extensive supplementary MD simulations were made using a 16 384-particle system. The simulations ranged from a determination of an effective pair potential for lead to simulation of the density correlation functions F(Q, t) and F s(Q, t), as well as the longitudinal and transversal current correlation functions J 1(Q, t) and J T(Q, t). The MD simulation «calibrated» via the experimental S(Q) and S(Q,ω) was used to prolong the range of neutron data to draw conclusions regarding such quantities as dispersion relations for the current correlations J 1(Q, t) and J T(Q, t), the generalized viscosity functions ν1(Q, t), ν1(Q) and νs(Q). Information regarding bulk viscosity νB(Q) is also gained. Conclusions are drawn regarding the relative importance of the derived pair potential form by comparison to corresponding hard-sphere data. The general framework of linearized hydrodynamic equations for the macroscopic situation transforming to visco-elastic equations of motion for finite wave-length and high frequency works well also for the case of a continuous potential. The region of transition from simple visco-elastic to hydrodynamic behaviour is occurring at wavelengths in the range (12÷20) Å for the cases studied. The spatial properties of the viscosity functions ν1(r), νs(r) and νB(r) are found to correlate well with the range of the radial distribution function for the liquid. The general results for liquid lead probably have wide range of applicability to other simple liquids with similar S(Q) and g(r) properties. © 1990 Società Italiana di Fisica.