Phonon softening and the anomalous thermal expansion of Ag(111)

Ab-initio density functional theory calculations are performed to study how the structure and lattice dynamics of the Ag(111) surface change with temp erature. It is found that the interlayer spacings near the surface increase dramatically at high temperatures, reversing the low-temperature inward co ntraction of the surface layer, in agreement with experimental data [P. Sta tiris, H.C. Lu, T. Gustafsson, Phys. Rev. Lett. 72 (1994) 3574.] This outwa rd expansion is accompanied (and driven) by a marked softening of surface p honon modes, as well as by large enhancements in the mean squared displacem ents of surface atoms. (C) 1998 Elsevier Science B.V. All rights reserved.