Computer "Experiments" on Liquid Metals

Abstract

The liquid structure factor $S\left(k\right)\mathrm{}$ and velocity autocorrelation function $\psi \mathrm{}\left(t\right)\mathrm{}$ 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 $S\left(k\right)\mathrm{}$ and $\psi \mathrm{}\left(t\right)\mathrm{}$ corresponding to a Lennard-Jones potential: The softness of the core increases the damping of the oscillations of $S\left(k\right)\mathrm{}$ and the oscillatory behavior of $\psi \mathrm{}\left(t\right)\mathrm{}$; the effect of the Friedel oscillations on $S\left(k\right)\mathrm{}$ and $\psi \mathrm{}\left(t\right)\mathrm{}$ 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 $S\left(k\right)\mathrm{}$ and the oscillations of $\psi \mathrm{}\left(t\right)\mathrm{}$. The dependence of the effect of Friedel oscillations of "realistic" amplitude upon their wave vector $2k_F$ is investigated in a simple model: In that model the height of the first peak of the structure factor, $S\left(k_0\right)$, is maximum when $2k_F=k_0$. The possibility of observing such a resonance effect by neutron or x-ray scattering on a liquid Li-Mg alloy is briefly discussed.