Surface structure in simple liquid metals. An orbital free first principles study

TL;DR

This study uses first principles molecular dynamics to analyze the surface structure of simple liquid metals, revealing ionic stratification and electronic density oscillations near their interfaces.

Contribution

It provides detailed first principles simulation results of liquid metal interfaces, highlighting structural and electronic oscillations across various metals.

Findings

Pronounced ionic stratification extending into the bulk.

Wavelength of ionic oscillations scales with Wigner-Seitz radii.

Electronic density oscillations vary phase with ionic profiles.

Abstract

Molecular dynamics simulations of the liquid-vapour interfaces in simple sp-bonded liquid metals have been performed using first principles methods. Results are presented for liquid Li, Na, K, Rb, Cs, Mg, Ba, Al, Tl, and Si at thermodynamic conditions near their respective triple points, for samples of 2000 particles in a slab geometry. The longitudinal ionic density profiles exhibit a pronounced stratification extending several atomic diameters into the bulk, which is a feature already experimentally observed in liquid K, Ga, In, Sn and Hg. The wavelength of the ionic oscillations shows a good scaling with the radii of the associated Wigner-Seitz spheres. The structural rearrangements at the interface are analyzed in terms of the transverse pair correlation function, the coordination number and the bond-angle distribution between nearest neighbors. The valence electronic density profile also shows (weaker) oscillations whose phase, with respect to those of the ionic profile, changes from opposite phase in the alkalis to almost in-phase for Si.