Computer simulation studies of the structures of the liquid-vapor interfaces of metals and binary alloys

The structures of the liquid-vapor interfaces of several members of a class of simple metals and their binary alloys (Na, K, Rb, Cs, Hg, Al, Ga, In, Tl, and Bi in Ga) have been investigated in a series of self-consistent quantum Monte Carlo simulations. These simulations are based on the pseudopotential representation of the electron-ion and ion-ion interactions as derived for an inhomogeneous metallic system. In all of the systems studied, the single particle density distribution along the normal to the interface is predicted to display stratification, with a spacing of about an atomic diameter, and with the amplitude of the density oscillations decaying to zero after about three to four layers penetration into the bulk liquid. This generic structure is very different from the corresponding structure in simple dielectric liquids. In the latter case, the longitudinal density profile varies monotonically across the liquid-vapor interface. The pair structure function in the plane of the liquid-vapor interface is predicted to be essentially the same as that in the bulk liquid. The use of a nonlocal pseudopotential in the self-consistent Monte Carlo simulations leads to very good agreement between the calculated and observed longitudinal density distributions. In addition, it is shown that a qualitatively correct description of the surface structure of a simple metal can be obtained from a simplified analysis in which model local potentials are utilized. This method bears the advantages of computational simplicity and physical transparency. The good agreement between theory and experiment for the systems reported argues for the validity of the results presented for all of the metals in this class, and the inferences drawn therefrom.