Origin of the Diverse Melting Behaviors of Aluminum Nanoclusters with Around 55 Atoms

Microscopic understanding of thermal behaviors of metal nanoparticles is important for nanoscale catalysis and thermal energy storage applications. Using first-principles molecular dynamics simulations, we reveal the microscopic origin of the diverse melting behaviors of Al$_{N}$ clusters with N around 55 [1,2]. The conceptual link between the degree of symmetry (e.g., T$_{d}$, D$_{2d}$ and C$_{s})$ and solidity of atomic clusters is quantitatively demonstrated through the analysis of the configuration entropy. The size-dependent, diverse melting behaviors of Al clusters originate from the reduced symmetry (T$_{d} \quad \to $ D$_{2d} \quad \to $ Cs) with increasing the cluster size. In particular, the sudden drop of the melting temperature and appearance of the dip at N = 56 are due to the T$_{d}$-to-D$_{2d}$ symmetry change, triggered by the surface saturation of the tetrahedral Al$_{55}$ with the T$_{d}$ symmetry.\\[4pt] [1] G. A. Breaux, C. M. Neal, B. Cao, and M. F. Jarrold, Phys. Rev. Lett. \textbf{94}, 173401 (2005).\\[0pt] [2] J. Kang, S.-H. Wei, and Y.-H. Kim, J. Am. Chem. Soc. (in press).