Layering at liquid metal surfaces and interfaces: Friedel oscillations and confinement effects

TL;DR

This study uses first-principles molecular dynamics to analyze sodium's liquid surface and interface, revealing persistent Friedel oscillations and ionic layering, with confinement effects influencing atomic arrangements.

Contribution

It provides detailed insights into electronic and ionic layering at sodium interfaces, highlighting the limited role of Friedel oscillations in atomic ordering.

Findings

Friedel oscillations persist across melting transition.

Strong ionic layering at surface and interface.

Confinement effects induce quasi-close-packed layers.

Abstract

The structures of the liquid surface and the liquid-solid interface of sodium have been characterized with extensive first-principles molecular dynamics simulations. Friedel oscillations in the electronic charge density at the free surface were found to persist across the solid-to-liquid melting transition, with a small but distinctive electronic layering that remains decoupled from the atomic positions. Strong ionic layering was observed both at the liquid surface and at the liquid-solid interface, notwithstanding the absence of Friedel oscillations or under-coordinated atoms in the latter case. Confinement effects at these soft or hard boundaries drive the atoms into quasi-close-packed layers; even for this prototypical free-electron metal Friedel oscillations are not relevant to ordering.