Surface layering and local structure in liquid surfaces

Recently, we performed a first principles molecular dynamics simulation of the liquid silicon surface, which showed pronounced density oscillations, similar to those in other liquid metal surfaces. Using the pair correlation function to characterize the local atomic environment, we compare those results with classical simulations of other liquids. We find that pronounced oscillations occur always in the correlation function, but that they are translated to density oscillations only when the liquid–vapor interface is very narrow. This narrow interface requires the formation of a well defined surface layer, whose local coordination shows a characteristic anisotropy, with enhanced in-plane bonds. However, the interactions responsible for this anisotropic bonding may differ significantly from liquid to liquid.