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

Abstract

Ab-initio density functional theory calculations are performed to study how the structure and lattice dynamics of the Ag(111) surface change with temperature. It is found that the interlayer spacings near the surface increase dramatically at high temperatures, reversing the low-temperature inward contraction of the surface layer, in agreement with experimental data [P. Statiris, H.C. Lu, T. Gustafsson, Phys. Rev. Lett. 72 (1994) 3574.] This outward expansion is accompanied (and driven) by a marked softening of surface phonon modes, as well as by large enhancements in the mean squared displacements of surface atoms.