Phonon properties of transition-metal clusters

Abstract

This paper is aimed at studying the phonon distribution for gold and copper clusters of different sizes and shapes. Icosahedral and fcc structures are considered. The clusters are regarded as classical systems interacting via a Finnis-Sinclair potential, thus neglecting the effects of the electronic degrees of freedom. The phonon spectrum influences several physical properties such as the specific heat and the thermodynamic stability at low temperatures. A careful positional analysis of the harmonic oscillations demonstrates the existence of phonons localized at the surface of the clusters. Those phonons prove to be responsible for an enhanced specific heat at low temperatures. In order to outline the effects related to the finite dimension of the aggregates, a spectral analysis of the dynamic matrix was performed in real space, thus avoiding the usual continuum approximations in Fourier space.