Bulk and surface vibrational and thermodynamical properties of fcc transition and noble metals : a systematic study by the continued fraction technique

Abstract

We present a systematic study of vibrational and thermodynamical properties of fcc transition and noble metals, using a model including central and angle-bending forces. The phonon frequency spectra are computed by means of the continued fraction technique; their knowledge enables us to calculate the contribution of phonons to various thermodynamical quantities such as the specific heat at constant volume, the entropy and the mean square displacements. For the bulk, our calculations reproduce all the experimental trends both qualitatively and quantitatively. Then we give results for the three low index faces of these metals. The surface spectra exhibit drastic deformations due to the existence of surface phonons. The variation of thermodynamical quantities due to the surface reveals some general trends. For example, the variation of specefic heat is maximum at a temperature which is a constant fraction (∼0.175) of the bulk Debey temperature. On the other hand, the lateral mean square displacement is much more dependent on the surface density of atoms than the perpendicular one Etude systematique des proprietes de vibration et thermodynamiques dans le cadre d'un modele comportant des forces centrales et des forces angulaires. Calcul des spectres de frequence de phonons, determination de la contribution des phonons a diverses grandeurs thermodynamiques: chaleur specifique a volume constant, entropie, deplacement quadratique moyen. Etude des trois faces de bas indice de ces metaux ou l'on constate l'influence de phonons de surface