Ab initio study of the atomic motion in liquid metal surfaces: comparison with Lennard-Jones systems

TL;DR

This study uses ab initio molecular dynamics to compare atomic motion at liquid metal surfaces with Lennard-Jones systems, revealing key differences in residence times and surface layering behaviors.

Contribution

It provides a first-principles comparison of atomic dynamics at liquid metal interfaces versus classical Lennard-Jones systems, highlighting unique surface phenomena.

Findings

Long residence times in metallic interfaces compared to Lennard-Jones systems

Surface layering observed in liquid metals but not in Lennard-Jones systems

Enhanced diffusion parallel to the interface in both systems

Abstract

It is established that liquid metals exhibit surface layering at the liquid-vapor interface, while dielectric simple systems, like those interacting through Lennard-Jones potentials, show a monotonic decay from the liquid density to that of the vapor. First principles molecular dynamics simulations of the liquid-vapor interface of several liquid metals (Li, Na, K, Rb, Cs, Mg, Ba, Al, Tl and Si), and the Na$_3$K$_7$ alloy near their triple points have been performed in order to study the atomic motion at the interface, mainly at the outer layer. Comparison with results of classical molecular dynamics simulations of a Lennard-Jones system shows interesting differences and similarities. The probability distribution function of the time of residence in a layer shows a peak at very short times and a long lasting tail. The mean residence time in a layer increases when approaching the interfacial region, slightly in the Lennard-Jones system, but strongly in the metallic systems. The motion within the layers, parallel to the interface, can be described as diffusion enhanced (strongly, in the case of the outermost layer) with respect to the bulk, for both types of systems, despite its reduced dimensionality in metals.