Temperature variation of surface phonon line width: low Miller index surfaces of Ag and Cu

Abstract

We have calculated the line width of phonons of the (1 0 0), (1 1 0), and (1 1 1) surfaces of Ag and Cu resulting from anharmonic terms in the interaction potential using time-dependent perturbation theory. The third-derivative term of the Taylor expansion of an analytic representation of a reliable semi-empirical potential mediates the perturbation to lowest order. Surface phonons with frequency less than 4 THz are found to decay predominantly via the phonon–phonon “difference” process, while those of higher frequency respond to the “splitting” process. At 300 K, the phonon line widths range between 1.8 and 0.08 THz and are found to be in good agreement with experimental data where available, and with the values deduced from accompanying molecular dynamics (MD) simulations, with a few exceptions. At higher temperatures the predicted linear variation with temperature in the perturbative results differs from that obtained from MD simulations.