The (110) surface was studied, at temperatures of up to 900K, by means of ensemble density-functional molecular dynamics techniques. The strong anharmonicity which was exhibited by this surface resulted in a negative coefficient of thermal expansion, where the first interlayer distance decreased with increasing temperature. Very shallow channels of oscillation for the second-layer atoms, in the direction perpendicular to the surface, supported this anomalous contraction and provided a novel mechanism for the formation of adatom-vacancy pairs; ahead of the disordering and pre-melting transition. This characteristic behavior originated from free-electron gas bonding at a loosely packed surface.

Thermal Contraction and Disordering of the Al(110) Surface. N.Marzari, D.Vanderbilt, A.De Vita, M.C.Payne: Physical Review Letters, 1999, 82[16], 3296-9