K. Pohl et al., ANOMALOUSLY LARGE THERMAL-EXPANSION AT THE (0001)-SURFACE OF BERYLLIUM WITHOUT OBSERVABLE INTERLAYER ANHARMONICITY, Physical review letters, 80(13), 1998, pp. 2853-2856
We have measured a large thermal surface expansion, 6 times larger tha
n the bulk, on Be(0001) using low-energy electron diffraction. This ob
servation seems to be inconsistent with previous measurements reportin
g negligible anharmonicity in the surface phonon modes normal to the s
urface. Density-functional theory calculations for the thermal expansi
on from the minimum in the free energy within the quasiharmonic approx
imation agree with the experimental observations and demonstrate that
the enhanced thermal expansion is caused largely by a softening of the
in-plane vibrations.