Self-consistent phonon approach to thermal vibrations in model small clusters.

Abstract

Thermal atomic vibrations in small clusters have been studied theoretically using the self-consistent phonon method. We have calculated the free energy for model clusters in which constituent atoms interact with each other through a pairwise potential and are vibrating with a frequency ${\ensuremath{\omega}}_{n}$ for the nth atom. Thermal softening and thermal expansion are investigated as a function of temperature for different structures of cluster sizes, N=7, 9, and 13. A structure with pentagonal caps is shown to be more stable vibrationally than a section of cubic structure of the same size. The instability temperature in the present model clusters is discussed in the context of melting in small clusters.