Structure and motion at the liquid-vapor interface of some interalkali binary alloys: An orbital-free ab initio study

We report the results of orbital-free ab initio molecular dynamics simulations of the liquid-vapor interfaces of three liquid binary alloys, Na1-xKx, Na1-xCsx, and Li1-xNax, whose bulk behaviors exhibit rather differing ordering tendencies. The study has been performed using samples of 2000 and 3000 particles in a slab geometry with periodic boundary conditions. In these alloys the total ionic density distributions along the normal to the interface display some layering with a virtually pure monolayer of the lower surface tension component located outermost at the interface. However, these systems have very different behaviors below the interface, which can be explained by their ordering tendencies in the bulk. The variations in diffusivity across the interface are, on the other hand, rather insensitive to the ordering properties, being dictated by the reduced atomic coordination at the surface.