On the existence of a nonmonotonic nuclear density profile at the jellium–vacuum interface

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Abstract
By means of a generalization of the method of Lang and Kohn, in which we allow the positive jellium to relax, we show that in the transition region between jellium and vacuum self‐consistent electron and positive charge distributions can, for large r s , have a nonmonotonic variation. For values of r s less than 4.3 we find monotonic charge distributions, while for values of r s greater than 4.3 we find nonmonotonic distributions. This trend is in accord with the expected decrease in screening with increasing r s of the electron‐positive fluid interaction. The widths of the positive charge distributions exhibit a nonmonotone variation with r s and are quite small, lying between one and two atomic diameters in thickness. This width compares well with that case of a dielectric liquid at its triple point where, taking argon as an example, the width is of the order of two atomic diameters. The monotone distributions, however, deviate markedly from the hyperbolic tangentlike form characteristic of liquid argon. Although the jellium model is strictly valid only at the absolute zero of temperature, we suggest the possiblity that for some liquid metals thermal motion might not be so large as to wipe out the structure in the positive ion distibution at the surface. We also emphasize the importance of a stable bulk phase to surface calculations.