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By means of constant-temperature, constant-pressure molecular dynamics, we investigate the crystal-to-amorphous transformation of the interrnetallic alloy NiZr2 resulting from the introduction of antisite defects. We constructed an n-body potential in the framework of the secondmoment approximation of the tight-binding description of the electronic density of states. This modeling of the interatomic forces is successful in reproducing both static and thermodynamic properties of the real material. The imposition of chemical disorder quantified by the appropriate value of the long-range-order parameter, S, engenders a volume expansion followed by relaxation to a stationary state characterized by lower density and higher potential energy. The behavior of the pair distribution functions, g(r), reveals that amorphization takes place for values of S 0.6, the corresponding volume expansion being of the order of 2%. Moreover the thermodynamic states obtained by chemical destabilization and rapid quenching from the liquid state are nearly identical.On the time scale of our simulations (10 ' s), no detectable long-range diffusion of either species follows the introduction of chemical disorder. Some relevant features of the pair distribution functions (first and second peak positions, number of nearest neighbors) are in good agreement with those obtained experimentally from amorphous NiZr2 samples generated by rapid quenching.

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The thermodynamical and structural behavior of a (110) face of a fcc (12-6) Lennard-Jones solid has been investigated by molecular-dynamics simulation on the solid-gas coexistence line. The temperature dependence of the relevant structural and mass-transport properties shows the following. (a) Despite the high degree of disorder which gradually appears on surface layers when the temperature is increased, the surface retains its solidlike character up to temperatures ( T=0.64m/k~) very close to the triple point ( T, =0.68m/kq). This conclusion does not confirm the findings of previous theoretical work predicting the formation of a liquid surface layer well below the bulk melting point. (b) The large concentration of vacancy-adatom pairs, produced at the surface in the hightemperature range, accounts for the high values of the surface diffusivity. (c) The Arrhenius plot of defect concentration indicates a progressive decrease of their formation energy for temperatures ranging from T, =0.8T to the melting point. Consistently, the order parameter decreases slowly with increasing temperature up to T, but from T = T" to the melting point it decreases much more rapidly than predicted by the extrapolation of the low-temperature data. These results are qualitatively consistent with the onset of a surface-roughening transition, in agreement with recent experimental results obtained from helium scattering on (110) copper surfaces.