Size-sensitive melting characteristics of gallium clusters: comparison of experiment and theory for Ga₁₇⁺ and Ga₂₀⁺

Abstract

Experiments and simulations have been performed to examine the finite-temperature behavior of Ga₁₇⁺ and Ga₂₀⁺ clusters. Specific heats and average collision cross sections have been measured as a function of temperature, and the results compared to simulations performed using first-principles density functional molecular dynamics. The experimental results show that while Ga₁₇⁺ apparently undergoes a solid-liquid transition without a significant peak in the specific heat, Ga₂₀⁺ melts with a relatively sharp peak. Our analysis of the computational results indicate a strong correlation between the ground-state geometry and the finite temperature behavior of the cluster. If the ground-state geometry is symmetric and "ordered" the cluster is found to have a distinct peak in the specific heat. However, if the ground-state geometry is amorphous or "disordered" the cluster melts without a peak in the specific heat.