Computer simulation of disordering and premelting of low-index faces of copper

Abstract

Molecular dynamics and the effective-medium theory have been applied to investigate the structure and dynamics of (110), (100), and (111) faces of copper in the whole temperature range from 0 K up to the bulk melting point, which has been determined to be 1240\ifmmode\pm\else\textpm\fi{}25 K. The observed order in the surface stability follows the order in the packing density. (110) disorders first via anharmonic effects (up to 700 K), then by vacancy-adatom formation and finally by premelting of the surface at about 1200 K. The (110) solid-melt interface is anisotropic and broadened, having a tendency to form small fluctuating (111) facets in equilibrium, which is suggested to be the atomic-scale melting mechanism in that direction. On the contrary, (111) is very stable up to the bulk melting point and even shows weak superheating effects. Premelting is also lacking on (100). The melting proceeds in these directions by a layer-by-layer mechanism. These observations correlate both with the experimental findings and with the thermodynamic models of the surface stability of fcc metals.