Computer "Experiments" on Liquid Metals

Abstract

The liquid structure factor $S(k)$ and velocity autocorrelation function $\ensuremath{\psi}(t)$ of classical systems of particles interacting by two-body potentials have been computed by Monte Carlo and molecular dynamics techniques. The two-body potentials were chosen with two features which might be present in the effective ion-ion potential of some simple liquid metals: a "soft" repulsive core of Born-Mayer type and long-range oscillations of the form $Acos2\frac{{k}_{F}\mathcal{r}}{{\mathcal{r}}^{3}}$. Comparison is made with $S(k)$ and $\ensuremath{\psi}(t)$ corresponding to a Lennard-Jones potential: The softness of the core increases the damping of the oscillations of $S(k)$ and the oscillatory behavior of $\ensuremath{\psi}(t)$; the effect of the Friedel oscillations on $S(k)$ and $\ensuremath{\psi}(t)$ is very small if their amplitude $A$ is of the order of that predicted by theoretical calculations. If $A$ is two to three times larger, Friedel oscillations increase the height of the first peak of $S(k)$ and the oscillations of $\ensuremath{\psi}(t)$. The dependence of the effect of Friedel oscillations of "realistic" amplitude upon their wave vector $2{k}_{F}$ is investigated in a simple model: In that model the height of the first peak of the structure factor, $S({k}_{0})$, is maximum when $2{k}_{F}={k}_{0}$. The possibility of observing such a resonance effect by neutron or x-ray scattering on a liquid Li-Mg alloy is briefly discussed.