We present a molecular-dynamics analysis of the stable nonmelting (100) and
(111) surfaces of Al. A many-body potential derived from first-principles
calculations is used. The molecular-dynamics method includes anharmonic eff
ects of all orders. We study static and dynamical properties of the surface
. An expansion of the (111) surface and a contraction of the (100) surface
results from the calculations. At low temperature, the vertical mean-square
vibrational amplitude is larger than the in-plane component, while at high
er temperature the in-plane component approaches the vertical one. Both com
ponents are at least twice as large as the bulk value. The interactions due
to the surface decay very rapidly going into the crystal from the surface,
as indicated by the analysis of the Debye-Waller factor. The evaluated lin
ewidths for the Rayleigh surface phonon reproduce quite well the temperatur
e dependence of the He-surface scattering data. The experimental behavior o
f the energy shifts, as a function of the scattering momentum transfer, pre
sents a minimum inside the Brillouin zone, which is also found by our calcu
lations. The surface energy shifts are about 30% larger than the bulk ones
at the same temperature. The effect of surface anharmonicity is much larger
for the static properties than for the dynamical properties. [S0163-1829(9
9)05924-X].