Oscillatory Surface Relaxations in Ni, Al, and Their Ordered Alloys

Results from simulations of Ni, Al, ${\mathrm{Ni}}_3$Al, and NiAl show long-range, oscillatory surface relaxations that decay exponentially into the bulk. Pure fcc Ni and Al have oscillation periods that are close to the nearest-neighbor distance, independent of crystal face. This is shown to be due to surface smoothing and steric effects. In ${\mathrm{Ni}}_3$Al and NiAl, the surface planes are rippled, with the Ni-Ni and Al-Al interlayer spacings oscillating 180° out of phase. Very good agreement between our results and experimentally measured atomic relaxations is obtained.