LONG-RANGE ORIENTATIONAL CORRELATIONS AT UNDERCOOLED LIQUID METAL SURFACES

The liquid surface of a reconstructing metal such as Au or Pt is expected to exhibit a higher surface lateral density as compared to an equivalent slice of bulk liquid. Using a realistic potential and molecular dynamics, we have analyzed the surface behavior of liquid gold as a function of temperature. The density profile along the surface normal develops, as a consequence, marked layering oscillations, while surface atoms are forced to a nearly triangular lateral packing. The undercooled surface, in particular, reveals the onset of very long-range sixfold orientational correlation [Formula: see text]. At the same time positional correlations do not vary appreciably. The growth of ξ6 upon cooling is dramatic near 1000 K, and the liquid metal surface appears to approach a transition into a hexatic phase at about 940 K. This temperature is, however, inaccessible to simulation, due to surface-initiated recrystallization on the nanosecond time scale.