Layering at liquid metal surfaces: Friedel oscillations and confinement effects

Abstract

The structures of the liquid surface of sodium have been characterized with extensivefirst-principles molecular dynamics simulations based on ensemble density functionaltheory. Friedel oscillations in the electronic charge density at the free surface were found topersist across the solid-to-liquid melting transition, and remain decoupled from the atomicpositions. Strong atomic layering was observed both at the liquid surface and at anartificial liquid–solid interface, notwithstanding the absence of Friedel oscillations orunder-coordinated atoms in the latter case. Confinement effects at these softor hard boundaries drive the atoms into quasi-close-packed layers; even for thisprototypical free electron metal Friedel oscillations are not relevant to ordering.